D700 AF problem

First of all, I apologize for posting a D700 question in a forum which does not have the D700 name in it. However, I hope that I am not far off as D800 is the D700 replacement.

That being said, after using the D700 for 3 months and loving it, I discovered a problem with it y'day. The following things need to happen to reproduce this behavior.

1. Lens AF is on.
2. D700 AF is set to back button, not shutter half-press.

3. AF at a particular distance, recompose, and then trip the shutter using the interval timer.

4. The camera changes the focus just as it does if AF is set on shutter half-press. Except, shutter half-press AF is disabled as in step 2.

Anyone else knows about this problem and how to work around it? I am afraid a lot of my good shots have been ruined by this behavior.

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Abhijit