PDF Split Feature - Random Failures

I use the pdf page split feature heavily in my job.  Every once in a while I get my work sent back because pages were not split correctly.

I pay close attention to pages when I use the split feature, and I noticed that about every three or four months the split feature starts splitting different that what I tell it to.

Example:

I have about 40 invoices that have to be split by 4 page intervals.  So I put the "4" in the box to tell it how many pages to split by.

The next day, I will have my work returned to me as none of the invoices were split by 4...they were split by 3. 

This has been going on randomly since I started this job, using Adobe Acrobat.  Most of the work I do is processing pdf's, so I use the split feature a lot.

It will be going ok for months, then all of a sudden, it will start splitting however it wants to, not how I tell it to split.

Then after a week to a month, it will stop and it will split the way I tell it to again.

Anybody else have this problem???

I know there are "bugs" in the program, and I'm wondering if this is one of them.