Thanks for filing the issue!

Able to reproduce the issue on reported chrome version 71.0.3578.98 and on the latest canary 73.0.3659.0 using Ubuntu 14.04 and Windows 10.
Note: Issue isn't applicable to Mac

As the issue is seen from M60(60.0.3112.0) considering it as Non-Regression and marking it as Untriaged.

Seems like a pretty good feature request to me.

What if the user wants to focus the omnibox but not leave keyword mode? 

Should ctrl+L / alt+D leave keyword mode 
(1) only when the omnibox is already focused or 
(2) regardless of omnibox focus? 

Option 2 has the minor user-inconvenience of having to know about and use the ctrl+e/k shortcuts.
For now, I'll work on making a CL for option 1.

Also worth considering, our help page [1] documents ctrl+L/alt+D as "Jump to the address bar", and does not imply leaving keyword mode. Perhaps, changing ctrl+e/k from "enter keyword mode" to "toggle keyword mode" would be a subtler solution for leaving keyword mode than changing ctrl+l/alt+d from "focus omnibox" to "focus omnibox and leave keyword mode".

[1] https://support.google.com/chrome/answer/157179?hl=en

To add to my previous comment c#9,
option 1 has the downside of inconsistency between ctrl+e/k which always enter keyword mode and ctrl+l/alt+d which leaves keyword mode only when the omnibox is already focused.
Perhaps option 2 is the better solution for now since it's the simpler state model.

Drive by: If the user hasn't typed anything beyond just going into keyword mode, then unfocusing will already take it out of keyword mode.

If the user has typed something, and unfocused, then currently ^L will return it to that state. I don't know why we'd want to change that. I do this occasionally. Also, OP was clearly referring to (1) given steps 2 and 3.

The Omnibox has very good focus state handling. This shouldn't require any weird bolt-on logic.

I was going to suggest that ^K could toggle keyword mode, but instead, if I'm using a keyword e.g. wikipedia.org, ^K will switch it to Google. That was unexpected to me.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0ab6826e3dfab1f31213713a718b68e15b8ab9ea

commit 0ab6826e3dfab1f31213713a718b68e15b8ab9ea
Author: manuk <manukh@chromium.org>
Date: Thu Jan 17 17:42:49 2019

[omnibox] Leave keyword with <ctrl>+L or <alt>+D if omnibox is focused

Prior to this CL, <ctrl>+L or <alt>+D would focus the omnibox, but leave it in
keyword mode if it were in keyword mode. Moving the cursor to the front of the
text and pressing backspace was the only way to leave keyword mode while
preserving user inputted text.

With this CL, pressing <ctrl>+L or <alt>+D while the omnibox is not focused
will, as before, focus the omnibox, select its text, and leave keyword mode
unchanged. Pressing those shortcuts while the omnibox is already focused will
leave keyword mode and, as before, select the omnibox text.

Bug:  918777 
Change-Id: I0efc1060b40c46bd51048de521958172dad83e45
Reviewed-on: https://chromium-review.googlesource.com/c/1413013
Commit-Queue: manuk hovanesian <manukh@chromium.org>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Reviewed-by: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623742}
[modify] https://crrev.com/0ab6826e3dfab1f31213713a718b68e15b8ab9ea/chrome/browser/ui/views/location_bar/location_bar_view.cc
[modify] https://crrev.com/0ab6826e3dfab1f31213713a718b68e15b8ab9ea/chrome/browser/ui/views/toolbar/toolbar_view.cc
[modify] https://crrev.com/0ab6826e3dfab1f31213713a718b68e15b8ab9ea/components/omnibox/browser/omnibox_edit_model.cc