Permalinks problem -> 4-digit IDs of posts

Dear WordPress,

I have a big problem with permalinks.

I’m trying to change address of the type: http://www.domain.com/post_id with address of the type: http://www.domain.com/2010/04/sample-post/

When I do that change, I wanna use the popular Permalinks Migration Plugin, which would redirect visitors from the old to the new address.

But that’s the problem: the plugin works perfectly with all posts, which have IDs of the type XX, XXX, XXXXX, but not with posts of the type XXXX – that is, 4-digit posts can’t be redirected to the new address and I get a 404 error.

At the same time, I have a heavy database query, and for that reason I’ve reverted to the old variant, until the problem’s solved.

To be concrete, here’s an example:

http://testing2.slusham.com/31310 – it works, http://testing2.slusham.com/174 – it works, while

http://testing2.slusham.com/2775 , http://testing2.slusham.com/4525 and any other 4-digit posts do not work.

I’ve also tried the plugin Permalinks moved permanently, but it fails just in the same manner.

Could you please tell me, where the problem comes from, how could I solve it, and whether it’s removed in the last WordPress version? Currently, I’m using 2.8.6

Thank you in advance for the kind support!