Autoblog. WTF with indexing? o_O

I`m done with 2 autoblogs.
Mentioned smth interesting.

Site`s pages are being reindexed several times a day.
One time I have 35 pages indexed?in 4 hours ? 57 pages. In 8 hours ? 38? and it circles and circles climbing up page by page.
Why it happens so?