Given that:
- A developer noticed that on Windows 10, FLAC tag changes in Windows Media Player's library don't seem to get written to file. To put it simple, there's a check in WMP's code that literally reads: "if the file's extension is flac, skip the step of writing tag changes to file". (link)
- On Windows 10, Explorer has issues displaying metadata of FLAC files (link);
- My observation: the property handle for FLAC seems to be broken and changing rating and tags does not work, neither does searching for rating and tags picks up the files if these were set with Opus or other third party programs. Even with third party property handles, these issues happen on the latest build.
Seems like someone at Microsoft really dislikes FLAC. Perhaps they would like to see users re-encode their libraries to WMA Lossless, but if that were the case, they would have broken the support to M4A too, as it is equally easy to convert to ALAC as to WMAL, but this one is fine, so it is probably utter carelessness from the quality control team and the developers.
They don't seem to be pushing WMA much lately so I can't see what they'd have to gain by sabotaging FLAC after it's already well established.