I have a single server installation of SharePoint 2010 with SP1. I have configured a Search Service Application and a content source to a shared folder. This folder has 1000 files with simple content (no more than 10 characters). Also, I created one scope with one rule using this content source.
After a first full crawl, it found 1000 items and the scope showed 1000 items. Then, run a second full crawl, it found 1000 items and the scope showed 2000 items. For each full crawls, the scope increases its count in 1000.
If I make an index reset and then repeat the previous sequence of full crawls, occurs the same thing.
This behaviour appears when the content source has more than 942 items. If there is less items, the scope never increases its count.
I made the same tests using a BCS as a content source and occurs the same thing and has the same limit, from 942 items the scope increments its count.
After that, I've updated my SharePoint 2010 with the CU June 2012 and didn't solve the problem.
Do you know why the scopes are increasing the count for every full crawl executed?