Alt+backtick not working as task switcher (possible bug)

Gossar

Test case:

Use US keyboard layout and a desktop environment/window manager that uses both Alt+tab and Alt+backtick to cycle tasks (such as GNOME, Budgie, Unity, OSX, or Windows with wincycle).
Open two or more windows in Vivaldi and open at least one other windowed application/program.
From one of the Vivaldi windows, press Alt+backtick (not grave deadkey). Do not release.
Holding the Alt key, repeatedly press the backtick as desired. Release all keys.
Press Alt+tab. Do not release.
Holding the Alt key, repeatedly press tab as desired. Release all keys.

Expected behaviour:
Pressing Alt+backtick should cycle between all open Vivaldi windows and only among Vivaldi windows.
Pressing Alt+tab should cycle between open applications/programs/tasks.

Observed behaviour:
Pressing Alt+backtick in Vivaldi does nothing until Alt is released, whereupon the main menu opens.
Pressing Alt+tab works as expected.

Suspicion:
Vivaldi either steals focus or fails to pass on to the DE/WM any "Alt+" hotkeys which it does not recognise (e.g., Alt+backtick).

Comments and observations:
This may be related to the problem underlying issues with Alt+shift and Ctl+Alt+arrows. The proposed solution to the Alt+shift problem, namely disabling "Alt Key for Main Menu", is a kludge and does not work here anyway--the menu may not appear but the hotkey is still not passed on to the DE/WM for task switching.

Possibly relevant threads (in the absence of a proper bug tracker):
Alt menu cannot be disabled

Typing after Alt+Shift opens menu
remove ALT shortcut

How to disable hotkey ALT, which leads to open menu of the browser

BUG: Setting ALT+F4 or SHIFT+ALT+F4 as a hotkey works but it still acts as exit...

Specifics:
Vivaldi 3.0.1874.38 (Stable channel) (64-bit)
Linux (Solus 4.1 Fortitude)

Gossar

Bug has been reported and was assigned the number: VB-68418.

codic

@Gossar I'm also on solus plasma (which is just awesome). I'm using the vivaldi-snapshot (can you test with this as well?) package instead of the standard vivaldi one, and plasma's alt+backtick works well. i also have mate and budgie installed so I can check in on their progress. just booted into both and they work perfectly as well. cannot reproduce