Update on this:
We're fairly certain this issue arises when one of our reception people answers a call on an analog line and places the call on hold, rings the person the call is for, and the intended recipient picks up the analog line prior to the reception desk phone being put back on hook. The busy lamp fails to clear in a timely manner in this scenario. Since my original post, I've updated our 7100 to 11.10.7.HA, and the behavior persists.
