Ooh, lock contention on the hardware CAM table or the software in the switch that handles these updates? The first time I am hearing about this bug :-)
It was a lock that was being held by software but also prevented hardware updates to certain hash locations in the CAM. So MAC addresses that hashed to those locations couldn't be learned by any means.
I wonder what hash was in use. Also, what workaround were you using to prevent flooding while this issue was happening?