I'm running 9.3.5 P2 on old Red Hat 7.3 server. BIND crashed today with
the following:
Aug 28 15:46:21 ns1 named[349]: mem.c:628: INSIST(((unsigned char
*)mem)[size] == 0xbe) failed
Aug 28 15:46:21 ns1 named[349]: exiting (due to assertion failure)

I started BIND again and it seems to be OK.
I'm not a programmer, so I only know that this is not normal behavior :-)
Is it a known issue, or do you need more info? This is a production
machine so I can't start debugging but I'll provide what I can.