This is probably because the the file type you're using doesn't allow saving tags to the file.
One way to prevent this is to share the library on one pc, the 'main' pc, where you will manage tags, import new files and do all your "work" on the library.
Both pc's need to be on the same network, wired or wireless, as long as they can reach each other.
Share the library by going to Tools, Options, Media Network. Check "Use media Network to share this library and enable DLNA". Follow the wizard and take note of the Access Key you will be given.
On the other PC, go to playing now, open Playing from ... and click Add Library. GIve it a sensible name and under Library Server, type in the Access Key. If all things go well, it should connect and play from the library shared on the other pc.
This is just a very quick rundown, I you run into trouble, just ask.