Ballistic: When you have this problem happen, is it in a Sampler channel? If so, copy the paino roll and paste it into any random channel, then replace the sampler channel with a new sampler channel, reload the .wav and repaste the piano roll notes into it. Sometimes the sampler glitches, especially during high load times like when you're loading alot of synths and then save and load a sample, it can bog down and not play the sample as a note sweep, but instead as a single shot with no pitch variation, a la drumkit. Just move the roll, replace, reload, then move back and it oughta work fine.