Cached memory never gets released [SOLVED!!!]

I've located the source of the leak.

Linux is innocent! Sorry for doubting you.

The problem is mozilla/flash allocates shared memory segments but doesn't get a chance to clean them up properly.

So:
Flash memory leak is present related to japanese fonts and our particular flash content.

We've installed a watchdog process that kills mozilla and restarts it once it uses up too much memory.

The watchdog process kills mozilla so mozilla doesn't have an opportunity to free up its shared memory allocations. They build up over time:
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status

0x00000000 3014673   root      666       1920000   0                     
0x00000000 1310738   root      666       1920000   0                     
0x00000000 2162707   root      666       1920000   0                     
0x00000000 5537812   root      666       1920000   0                     
0x00000000 3866645   root      666       1920000   0                     
0x00000000 4718614   root      666       1920000   0                     

When I ipcrm these the cached memory goes back down to normal levels.

Thanks for everyone who responded, and sorry for wasting everyone's time.

-Dave