I am also struggling to reproduce it with a custom test file. All I can say is that I've run into the issue multiple times on live files. Indeed, on EVERY file since i started this little experimental dive into 7.4.2.
I can also say that opening the first file in the document, closing all other files, and hitting Restart on the search eliminates the issue, hence my original question about a keyboard shortcut. While I don't know the exact conditions for replicating the problem, I do know the sufficient condition for resolving it.
EDIT: RE: Sigil's utility as an OCR correction application, I certainly haven't found a better one. OCR errors are highly compatible with RegEx for identification and, in many instances, correction.
EDIT 2: Figured out how to replicate.
See post #21 below