BuddyPress.org

Your posts should still be at http://mydomain.com/whatever/post. The url http://mydomain.com uses the home.php template in bp. That overrides index.php that is used if home.php doesn’t exist. If home.php exists in the theme directory the only way to run index.php is to trap something like ‘blog’ and then load that index.php template.

This is normal behavior for any wp theme that uses home.php. bp doesn’t change the permalink structure of your blog.

You can not use home.php if you like by deleting it from the theme directory or renaming it to something like home.php.off

That will get you index.php being used.