I get this too when using Chrome on Linux, Ctrl-Backspace does not work but Alt-Backspace does. However, on the same Linux machine, when using Firefox Ctrl-Backspace does work, and Alt-Backspace does not. This has been going on for months now, so it is across several versions of Chrome, the most recent of which is 51. The same goes for Ctrl-Delete to delete one word ahead of the cursor - it is swapped with Alt on Chrome+Linux, but works correctly for Firefox+Linux. Bizarrely, on Chrome+Linux, Ctrl-Left/Right Arrow will skip words correctly. That Alt-Backspace works makes me wonder whether somehow the Web Client thinks it is on a Mac system, and the client is expecting a Command- modifier which is why it works with Alt? Maybe Chrome and Safari are being conflated due to their WebKit origins? I would have expected that correct operation of these keyboard shortcuts should have required zero intervention on the part of the programmers, shouldn't this stuff be handled by the operating system? Anyway, I hope I've helped, and that you can speedily fix this bug.