Some days ago I ran into a major problem. Configured PIM dense mode on my virtual devices, everything looking fine. ICMP requests to the MCast groups were successful until…from one second to another it did not work anymore. My EIGRP adjacencies were flapping and I experienced packet loss. I could not say were the packet loss was sourced.
I described it here: http://ieoc.com/forums/t/18290.aspx
There is a link on the web, where this trouble is described as well: http://ieoc.com/forums/t/3488.aspx
If you gained other experiences…tell me!