On 3.2.4-5 they made a setting change that forces whatever you set on your queue for music on hold to be the music on hold that the call carries over until its end. So if you have Ringback set in your queues, and one of your agents answers the calls and puts that call on hold, they will get the ringback tone for the music on hold. If you set actual music on hold in the queue that is the one the call will use if they are put on hold.
I have a related post here: Default music on hold not being respected. - #8 by hlev