@OddCosine - just to add it is not "theme" related. As theducks hinted at earlier Kovid completely replaced the combobox implementation with a new one in 0.8.60. This was I believe an attempt to bypass the crashing issues which a few users had reported here on the forums. As to what will or won't be changed further about it's behaviour I leave that up to Kovid
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Other than things I reported which Kovid has fixed, my biggest behaviour difference that I have noticed is trying to rename say an author name which has incorrect casing. You have to keep hitting escape to cancel the dropdown portion to stop it "fixing" your correction.