Hi Stas,
Ok, after more investigation I found it is not a MySql specific problem. Basically what happens is that whenever you tab out of the Title field it tries to suggest an url and since the current url already exists it appends numbers to make it not duplicate. The problem has been there for a long time but became more apparent because I added javascript to set the focus on the title textbox, whereas before you may never have entered that field when updating a blog post so it did not happen as often. I will fix this, but for now you can be aware of it and after you tab out of the title and you see the url change, just change it back as it was before saving.
Best,
Joe