No dump after double panic

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

A few days ago, I again hit a presumably quota-related panic on our 4.0/amd64
file server (page fault trap at dqget+0xee). Luckily, this was at a time where
I could afford the delay of taking a dump. So I did a reboot 0x100 and got a
second panic (locking against myself, I was too slow to note details) during
sync, and the machine rebooted without taking a dump.

Is this intended bevaviour? If yes, why? If no, could it be changed?

Regarding the original panic, I only have a photo of show registers, notably
both rdx and rax are zero at a cmpq 0x80(%rdx,%rax),%rpb.