No I haven't. I've been testing this on the latest snaphot and also the M4 release using the default configuration. I was sending up t o 1000000 messages to a queue with 2 slow consumers.. Message backlog has already reached more than 500000 and still havent been able to reproduce the issue. I also tried restarting the broker and consuming again the backlog messages. Doesn't seem to have any issue from my end.
Btw, for the consumer clients, I'm using the sample clients that is shipped with the distro.