Most likely you're not getting an open loop disconnect signal from the telephone company. A caller in the auto attendant hangs up without selecting anything, the auto attendant waits for input, the telco sends new dial tone, which times out and reverts to the "please hang up and dial again" recording, and the auto attendant times out and transfers the call to the operator.
Monitor a line with a butt set and place some test calls. Put yourself on hold, then hang up and see if the hold releases. See if it is all lines, or just some lines.
Contact the telephone company if you find it is a hold release issue.
