Unexpected long tone when blind transferring a call using a shared line in VVX 450

When receiving a call to line 1 on the register phone, a second call is placed and completed pressing the attendant BLF key for a Blind Transfer. The active call is transferred and inbound call is ringing, but you can hear an underlying tone until the inbound call stops ringing. 

Upgrade to UCS 6.4.1 or UCS 6.5.1.