ERROR:  heap_delete: (am)invalid tid

I am using 6.4.2 postgresql from a Mandrake rpm.  That I cannot change
:(.

Is this a bug? I get it some times when deleting a record.  This is
happening inside a C program and it segfaults after writing this error.
It is hard to reproduce, but it happens.  Any old dogs know what this
means?

ERROR:  heap_delete: (am)invalid tid

thanks,
james