Midi tracks not time-aligned to each other

Hello, I have a problem with two midi tracks that are not aligned, ie. the playback of track 2 is slightly slower than track 1. I recorded track 1 first then track 2 later while track 1 is playing. I have cubase studio 5 hooked up to the clavinova cvp509. It also seems that if I shutdown cubase and restart, the problem goes away. But after running Cubase a while, I see a delay starting to creep into my new tracks again.

Any ideas? Let me know if you need any other info to help diagnose my problem.

Thanks in advance.

Not sure, if I got it right, but according to this:

it may be classic MIDI timer problem. See this article:
http://www.soundonsound.com/sos/dec07/articles/cubasetech_1207.htm

Thanks! You nailed it!