Search highlight is not always rendered

Sometimes, when searching for text is active, some of the instances of the found text are not fully highlighted - only the yellow box around the text is visible, while the background of the test is not highlighted. See the attached screenshot - two of the found instances of "prev_end_pos" on lines 182 and 185 are not properly highlighted.

I don't know the exact criteria for the text to be not highlighted, but it seems like the problem is stable (i.e. cancelling the search and searching for the same text again yields the same result). This is not a low level drawing issue - scrolling the text off the screen and back again does not fix the background.

I expect the highlighting to be reliable as I often use it during code editing. Missing highlighlting makes it easy to miss an instance that needs to be edited.