airplay sound not mirroring after first time until restart

Anyone else seeing this issue?

When we connect either the iMac or the MacBook Pro to our 2nd generation apple tv via airplay the first time, the sound goes to the tv as expected.

If we try to use airplay a second time, the sound stays on the computer, though the picture shows up on the tv. If we try to change the sound in preferences to the apple tv, the airplay connection is broken. Once we restart the computer, the sound works as expected.

All of the latest system software updates have been applied.