postmaster dies

Hi,

Every now and then the postmaster dies without reason.
I'm using vanilla 6.2.1 under Linux 2.0.33 (libc 5).
I also make use of large objects.
gdb and the core file says that the crash is happening in free().

Does anyone have a clue? 

#0  0x810ae53 in free ()
#1  0x80e609e in AllocSetFree ()
#2  0x80e6583 in pstrdup ()
#3  0x80e62a2 in MemoryContextFree ()
#4  0x80e647d in pfree ()
#5  0x80c618d in HandleFunctionRequest ()
#6  0x80c7768 in PostgresMain ()
#7  0x8095d03 in main ()
#8  0x80648cb in _start ()

Thanks in advance.
Maurice