String input via input method is not rendered properly in the overview search box

This is an upstream report of https://bugzilla.redhat.com/show_bug.cgi?id=2062660 . As described there, if you select an input method (e.g. Anthy for Japanese) and then type into the search box in the overview, the pre-edit string is not rendered properly. If you e.g. hit the keys 'y', 'a', 'm', 'a' it should first show 'y', then 'や', then 'やm', then 'やま' (and then if you hit space, give you a completion list). But it fact it just shows 'y', then stops updating with subsequent keypresses.

Oddly, I can't reproduce this on my own laptop, where I have US English keyboard layout and Anthy input method configured. But the downstream reporter hit it, and our openQA automated testing hits it every day. Not sure what the difference is there.