Then it IS assigned to Auto VM Coverage, (or the Transfer Return Extension setting for the VM/AA ports are NOT set to 10) but there ISN'T a mailbox 36 in the system.
Call rings at 36, isn't answered, returns to VM, can't find a matching mailbox, "your call is being transferred", now transfers to Ext. 10.
Depending on the flavor of voicemail you have, create mailbox 36 and you're set.