Regression: music stops working in long-running client

I've seen this happen twice now since patch; never saw it before.

Two different clients, having run for 24+ hours, suddenly stopped having their music working at different times. The SFX still work fine, just no vendor music, combat music, zone music, etc.

In both cases, the other clients running on the same PC at that time worked fine. Only the one client stopped working.

This has now happened two different accounts at different times. The third client which was started at the same time has not had it happen yet.

Camping to character select does not solve it (no music plays there either). You have to totally close the client, and then restart it. Then all is fine.

Perhaps this is an old bug, but I've never seen it before, and now it's popped up twice in a matter of a few days...