Yes, it's Word 2010. I have been using this for 10 years, on documents professionally (publisher) formatted, documents formatted by highly organized nonprofits, and documents prepared by publishing amateurs, and I have never seen this before. MS isn't supporting W2010 any more but I'm sure I saw a Win7 update the other day; maybe I should uninstall that, although as it was a purely security-oriented update I don't want to.
I misled you slightly, I think, without meaning to. Open new document/copy and paste a sentence with italics from troublesome file/delete itals--not tracked, although the TC options were set to track formatting. Open new document/copy and paste a sentence with itals from a file where TC did track correctly/delete itals--tracked. I don't know how much formatting Word 2010 carries to a new file with a simple copy-and-paste but the sentence from the "bad" file is the one for which the change from italics to roman was not tracked.
Are you suggesting that Word 2010 and Word 2016 or 2019 (I don't know what the formatters are using) have weird incompatibilities of which this may be one? I know Office 2013 did not play well with others.