The recent iTunes updates 9.2 and 9.2.1 have a bug. At this point we advise you not to upgrade if the genre classification of your music is important to you.

The Bug
Some songs after being played will have their genre changed to a number in parenthesis. The genre will change to the numerical equivalency according to the id3v2.3.0 specification.

Some are reporting success in fixing the problem by converting (or reapplying) the ID3 tags to ver. 2.4. This is done by right clicking (or Control click) on the song and selecting "Convert ID3 Tags". Our own experience with this has been mixed. We would greatly appreciate hearing from you on this.

While this bug is an inconvenience or huge annoyance depending on the size of your music collection, we don't believe it damages your files. Once Apple releases a patch, we expect the genres to be automatically switched back.