The design of current logic:
When you change resolution of monitor A, a notification with "revert" button will pop up (The notification never timeout if you don't click on it.). Before the notification disappears, the resolution change of monitor A can be reverted either by click "revert" button or change monitor B's resolution.

This seems to be a weird design. I think we can either add an "accept" button to the notification or finalize the change for monitor A when we start adjust B's resolution.

Either of this requires UX point of view.

I just reproduced this and the "revert" button is irrelevant; acknowledging it or not doesn't make any difference.

This issue is just: try to change the resolution of one monitor and ChromeOS will sometimes change the resolution of the OTHER monitor too to some random value for no obvious reason/without any obvious logic.

I just reproduced this with MST but that doesn't seem to matter either because the original reproduction was without MST.

It really doesn't help that ChromeOS offers no control on and even hides really hard the refresh rates. In fact I suspect that the "smart" refresh rate selection could be where this bug is; maybe it's not designed/prepared for multiple external monitors.

+malay who is working on changing the resolution settings.

I found another bug: when using MST the display settings panel can simply not be trusted. In the first screenshot the popup is correct and the display settings is wrong.
The second picture attached is taken after merely closing and re-opening the display settings. Now a different resolution is shown - still wrong.

This different bug seems MST specific though.

Deleted: display_settings_wrong_resolution.png 164 KB

	display_settings_wrong_resolution.png 164 KB View Download

Deleted: wrong_resolution_2.jpg 2.6 MB

	wrong_resolution_2.jpg 2.6 MB View Download

> This different bug seems MST specific though.

In fact it's not MST specific, two monitors are enough. Eventually I got the display settings to show me wrong values even with MST disabled and one monitor connected on each Type-C port (PixelBook R65-10290.0.0). I don't think I ever saw any wrong resolution reported by the popup but I could have missed that.

BTW here's a command useful to find the real resolutions:

  grep -A1 connected, /sys/kernel/debug/dri/0/i915_display_info 

A different but probably related issue is the lack of chooser when there are more than 3 screens:  issue 698290

I thought getting the display settings to report a wrong resolution required two external monitors but no: just observed this again with a single external monitor this time, see screenshot. So two external monitors seem to just trigger that bug more frequently. Again the popup is correct while the settings is wrong.

Interestingly, the settings report a resolution mode that isn't even listed as supported by modetest -c

Deleted: Screenshot 2018-01-29 at 2.47.19 PM - Display 1.png 173 KB

	Screenshot 2018-01-29 at 2.47.19 PM - Display 1.png 173 KB View Download

In response to #8
The resolution you see on the settings page is the Hardware Resolution with the device scale factor applied. On the other hand, the notification only displays the Hardware resolution.

In this particular example, the device scale factor is 1.25. (3072 * 1.25 = 3840)

Thx, I thought scaling was only for eDP panels (where it is the only option anyway).

So for external monitors how can you predict/control/tell whether scaling will be active versus not? I tried the "stats for nerds" in Youtube but ended up even more confused.

Scaling was added temporarily for 4k displays. I believe there are only 3 scales currently supported for 4k external displays. 1, 1.25 and 2. There is no way to differentiate between them right now, unless you change the slider on display resolution settings and try them one by one. 
An easy way to check what your current device scale factor is by visiting https://bjango.com/articles/min-device-pixel-ratio/

Display resolution will be replaced with a “display size” option in M66 (is in experimental for M65 and can be accessed via chrome://flags). This will solely control device scale factor of the display instead of resolution. Resolution on the other hand would be presented as an advanced setting for external disolays.

> An easy way to check what your current device scale factor is by visiting https://bjango.com/articles/min-device-pixel-ratio/

I just tried this page on a fixed 1920x1080 eDP panel (cave) and I couldn't make sense of it.
When cycling through all the scaled(=fake) resolutions from 960x540 to 2400x1350 this page always shows the same values except for one resolution: 1536x864. Why is just this one different?

For 1536x864:
-webkit-min-device-pixel-ratio 1.2
-o-min-device-pixel-ratio nothin’
min-resolution (dpi) 115dpi
min-resolution (dppx) 1.2dppx

For all other fake "resolutions" from 960x540 to 2400x1350:
-webkit-min-device-pixel-ratio 1.0
-o-min-device-pixel-ratio nothin’
min-resolution (dpi) 96dpi
min-resolution (dppx) 1.0dppx

"-webkit-min-device-pixel-ratio 1.2" says that the device scale factor is 1.2. (Its actually 1.25, but the website only gives it upto 1 decimal point)

It means 1536x864 is a "fake" resolution and is actually just 1920*1080 hardware resolution rendered at 1.25 device scale factor.

All the other resolutions are actual hardware resolutions provided to the system by the display hardware. They all are rendered at the device scale factor of 1.0

> All the other resolutions are actual hardware resolutions provided to the system by the display hardware. They all are rendered at the device scale factor of 1.0

No; as I wrote above this is an eDP panel and it only supports 1920x1080. This is confirmed by grep -A1 'connected,' i915_display_info AND "modetest -p | grep driver" throughout all pseudo-resolution changes. This is with cave image R65.0.3299.0 / 7820.347.0

Long story short this test page doesn't seem to work with eDP panels. On the other hand it does report correctly and as you predicted the scaling factor for the *external* 4K monitor I tested in comment #8.

> unless you change the slider on display resolution settings and try them one by one. 

I found that left and right keyboard shortcuts offer a practical and even convenient way to try resolutions one by one, including the scaled ones. None of them reproduces the very first screenshot attached to comment #5 (it would be 1.5 scaling if it were scaling)

> Display resolution will be replaced with a “display size” option in M66 [...] This will solely control device scale factor of the display instead of resolution...

Sounds like a nice simplification, looking forward to it.

 issue 822248  looks like a duplicate