I have a Verizon and was using their new OS 5.91 and noticed an issue with voice notes. So I switched down to MTS Mobility's issue of OS 5.0 and still have it.
When I record a voice note as long as my memory card isn't in it operates correctly. When I put the memory card in it lags when trying to stop it and will often keep recording for 20-30 seconds. Also, I've yet to find a way to set a default recording as the phone memory and not the memory card.