Hi Huw,
did you actually test it? I tried this https://testbot.winehq.org/JobDetails.pl?Key=126114, which doesn't suggest that. May be I got the test wrong?
Note: - I also tried to check if we could get rid of the direct unicode comparison in compare_wstr, as it looked better to me to have only a single test strategy (unicode => multibyte => unicode) - but if we need to go back to default (ansi or oem) cp from lcid, then we havea detect locales without codepages (hence requiring the two tests above)