I have 2 different libraries open on different computers.
Both libraries point to the same files.
On Computer A I removed the keywords associated with a particular podcast mp3.
I waited until MC said that the file had been updated (update tags is on).
On Computer B, I selected the file in the library and did Update Library from File (tags).
The keywords remain.
I double-checked that the file itself had a new modified date of today, and it did, just in case that is the basis on which libraries get updated from file tags.
I repeated with 6 other files and had the same result.
While it never worked with the keywords field (the field is set to save to tags), it did work with a Rating.
I'm running 15.095 on both computers. I didn't see anyting in the various histories of the updates that has addressed this.
Edit: I just did another test. If I manually select Update tags from library on a file I just modified, then on the other computer select update library from tags it works. This leads me to believe that when MC says it is "saving tag changes" automatically when a change is made (this is selected in options), it isn't really updating the tag after all. So still a bug, just a different one. Hopefully someone could reproduce.
Yet another edit: it worked fine with a single file for which I manually updated the tag from library, but when I did this for a batch of 6 files the update library from tags on the other computer still didn't work. Very odd indeed.