Hi Scott,
I am not sure whether the TAC engineering working with you informed this or not but this is what I read on the case comments: "When there is a disturbance on the wireless network and clients start associating and disassociating quickly, the large number of association requests received could cause the stm notification queue to get full for very short times. During such times, any 'assoc req' received will get dropped and a log like the one in question get fired. However, such event is not serious, as the client wireless driver will resend another association request in a matter of milliseconds."
If you have more questions, I would recommend going through the same TAC engineer, as your ticket is already open.
Thanks