Customer upgraded CS1000 to 5.5 and now on their M3905 sets the phones remain off-hook after a call. User must disconnect the headset for key to release. This problem is causing incoming calls to buzz instead of ringing normally when they're not on the phone. Customer said this started happening after their upgrade to 5.5, prior to that it was not an issue. Anybody heard of this or know of any patches to fix it?