I truncated core_url_rewrite table then in Index Management section I click on Reindex Data link for Catalog URL Rewrites.

In URL Rewrite Management section I get now 17 records found. See the bellow:

Let's Reindex Data again Catalog URL Management. Without making any changes in products I get more 3 records. See the images bellow:

After Reindexing Data two more times there are now 23 records found. Please note in the image bellow all these 6 records are "Custom" and RP to similarly links like pointers in programming.

Why is this happening? Normally if there are no changes I should get the same records. Why before Reindexing Data Magento doesn't truncate core_url_rewrite table? In this way always the data in here will be fresh? If you have 2000 records with every reindexing of your data you will get more and more records. Is this a bug?

Thank you