Hi,
Thanks for the bug report with steps to produce it. I will investigate this and fix it today.
I will add a web config setting that will allow forcing a prefix like username-post-title.aspx, the friendly urls are not designed to simulate folders.
Or perhaps appending the date to the end of the post title like post-title-2009-05-05-05-10-90.aspx would solve it more naturally.
The Web.config setting will be disabled by default because probably a lot of sites are not hosting a bunch of blogs and would rather not have the prefix in the url, but this will allow that scenario of lost of blogs and avoid url collisions.
Best,
Joe