I have heard that GZipFilter has problems when the app server applies it more than once to a request -- for example, when there are server-side forwards. This definitely happens when using Tiles.
If I may be so bold as to plug my own work, I have created an open-source compression filter that is faster, cleaner and more comprehensive than GZipFilter. It does not suffer from the problem described above. If you are still having trouble, maybe you can give my filter a try?
PJL Compressing Filter
http://sourceforge.net/projects/pjl-comp-filter/