Really weird problem that doesn't make any sense. Help?

This is reaallyy weird, and I can't find it anywhere online. I'm posting it on here since it seems to only be happening on this DAW. I recently got an Apollo Twin Duo audio interface. Installed it, got it working right, and everything works fine. However:
 
Say I record an audio file (a vocal track for instance) and don't touch it, or do anything to it. I save the file, close it all down, and let it sit. The next day I go on, that very same vocal track is now lower in pitch. Nothing too drastic, but noticeably lower. I leave it be, and the next day, it's even LOWER. Now that vocal track is sounding like an evil demonic entity talking to you... it makes no sense.
 
This became a problem because I spent all last night working on an instrumental and I come on today and all my instruments are out of tune and sound way deeper in pitch than they were (and I proved this by recording a fresh clean recording of the same thing, and played them together, and they don't match. They are different pitches completely.)
 
Will add in: nothing seems to be off with the sample rates. When I open the ASIO panel in Sonar, my Apollo has the same sample rate as the one listed in the properties for Sonar.
 
No idea why this is happening. Any ideas?