Changing the status to Untriaged, so that the issue would get addressed.
Thank You.

Very strange. This only triggers when you first move one of the sliders using mouse (using keyboard doesn't repro, nor does going to the subpage then trying to click the back arrow).

Discovery:
Apparently it doesn't just break the back arrow, but all sorts of keyboard interaction with buttons.

- you move the slider with mouse
- shift tab to the search button, press enter
- type in something and press tab again to go to "x" for clearing the field 
- press enter and observe it doesn't work.
- shift tab back to the field, ctrl + a to select all and backspace to delete.
- notice you're on the basic page now. Tab to any item's subpage arrow
- press enter and notice that it doesn't work.

More discovery:
- It also doesn't break when you click on the grey-bar somewhere.

So it ONLY happens when you mouse-drag the knob.

I was able to create a minimum repro. on jsfiddle with just a plain paper-slider + a native button. Filed an issue with Polymer: https://github.com/PolymerElements/paper-slider/issues/186

Will give them a few days to investigate first.

I was talking to Keanu, and they have found the issue, and there needs to be a fix in Polymer. but they think it's a low priority issue, so if we disagree, we can either ask them to raise the priority or make a PR.

Also, I just tested with paper-toggle, and the same bug applies. i.e. if you drag the toggle to toggle it, then subsequent Enter-key events will not be recognized.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ea73b1f7ddc1a243ad5886a2aa909f91eb492974

commit ea73b1f7ddc1a243ad5886a2aa909f91eb492974
Author: scottchen <scottchen@chromium.org>
Date: Thu Jun 01 02:07:05 2017

MD Settings: Fix dragging slider bugging out the Enter key.

There's a bug in the Polymer gesture code that prevents "keydown" to be
recognized after the "track" (unless "mousedown" happens and resets the
prevention state).

Manually calling Gesture's reset function will fix the issue. This should be
considered a temporary fix until Polymer fixes the gesture code.

BUG= 706709 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2864563002
Cr-Commit-Position: refs/heads/master@{#476151}

[modify] https://crrev.com/ea73b1f7ddc1a243ad5886a2aa909f91eb492974/chrome/browser/resources/settings/controls/settings_slider.html
[modify] https://crrev.com/ea73b1f7ddc1a243ad5886a2aa909f91eb492974/chrome/browser/resources/settings/controls/settings_slider.js
[modify] https://crrev.com/ea73b1f7ddc1a243ad5886a2aa909f91eb492974/chrome/browser/resources/settings/controls/settings_toggle_button.html
[modify] https://crrev.com/ea73b1f7ddc1a243ad5886a2aa909f91eb492974/chrome/browser/resources/settings/controls/settings_toggle_button.js