Unable to reproduce the issue on Win-7 and Win-10 using chrome reported version #61.0.3163.100 and latest canary #63.0.3230.0.

Attached a screen cast for reference.

Following are the steps followed to reproduce the issue.
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1. Typed localhost:8000/ in address bar with setting for "Use a prediction service to help complete searches and URLs typed in the address bar" turned off.
2. Pressed alt enter to open a new tab.
3. Observed that a new tab opened at localhost:8000/ 

Reporter@ - Could you please check this issue on latest canary #63.0.3230.0 by creating a new profile without any apps and extensions and please let us know if the issue still persist or not.

Thanks...!!

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I have been able to recreate the behavior on a new profile, on a fresh install of canary. It's !sometimes! working correctly when the prediction service is turned off from the start. Once you enter the wrong webpage once, it's always entering the www.localhost.com:port/. It's not unfeasible to enter it, since when the prediction is turned on, that's the correct behavior. Deleting all info (cookies, history, etc) does not help. Creating a new profile sometimes helps, hard to say when, but certainly not always.

Attached - new profile, with localhost:7001/, entering it regularly is fine, entering it via alt + enter adds www. and .com

Version:
63.0.3231.0 (Oficjalna wersja) canary (64-bitowa) (cohort: 64-Bit)

Avast online security shown on the video is not the culprit btw, the issue originated at work, where avast is not adding the extension, just testing it at home. 

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Thank you for providing more feedback. Adding requester "krajshree@chromium.org" to the cc list and removing "Needs-Feedback" label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Tested on latest Stable #61.0.3163.100 and latest canary #63.0.3230.0 on Windows 7 and Windows 10 and not able to reproduce the issue. Attached the screencast for reference.

Could someone from Dev please look into the issue.

Thanks!

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Correction in C#5, Latest Canary #63.0.3236.0.

Since TE doesn't able to reproduce this issue, adding TE-NeedsTriageHelp label for further triage

adam.popanda@,
the behavior you're describing is exactly what would happen if you pressed control-alt-enter.  Are you sure that sometimes you're not accidentally pressing both control and and alt at the same time?

If you're sure, could you try again with a different keyboard plugged into your computer?  Maybe your keyboard is acting up.  (What brand of keyboard is it?)

Or perhaps you have alt mapped to alt+control in Windows?

Please investigate and let us know, as we cannot reproduce this.

I'm certain, that I'm only pressing the right alt, and enter. What is funny, is that it seems, that pressing left alt and enter seems to be working fine. I didn't bind control - alt to alt, and pressing "right alt + delete" doesn't launch task manager, so it seems, that it isn't bound to alt + control. 
The keyboard is fine, since the issue persists both at my work, and at home. I have a generic logitech keyboard, K120. At home I have a Dell, don't remember the model. I'm using the "Polish programmers'" language in windows. Seems to be, that "AltGr" might be causing problems here. Still, I don't think this should be the indended behaviour?

Thank you for providing more feedback. Adding requester "mpearson@chromium.org" to the cc list and removing "Needs-Feedback" label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Thanks for the clarification that this is problem with the right alt (a.k.a. altgr).  That reminds me of bug 247297, which sounds like exactly this issue.  Merging there.  Sadly, it sounds hard to fix, so you probably should just practice using left-alt. :-(

(If you're curious about the technical details, see comments 17 and 19 on that bug.)