I am not sure if this is a bug or a feature but it looks
like in RH 6.x no user can be in more than 32 groups. If
they are put into more than 32 groups they will no longer be
able to logon to the machine. The groups capmmand will
report only 32 groups for the user.
It's a kernel limit. See /usr/include/asm/param.h.
You could in theory change this in the kernel, but
a large portion of userland may need to be recompiled because
The big effect of changing this is that you're changing the
size of the kernel's internal task strucutre, so each task will
take a little more kernel memory.