incorrect url rewrite in 3.0.1

It started to happen after upgrade to 3.0.1. While forums got really faster, some of my users started to report errors, like this report:

Here's the deal. I launch http:/www.xxx.com/forum

Within 2 seconds, the 'not found' error message appears and the url becomes the one with %20.
I will then backspace the url to only http:/www.xxx.com and relaunch.

This happens twice. (2 attempts)

The third attempt usually works.

Sometimes, sometimes not, while I'm "in the forum", it will do the %20 thing again and then I have to start over. For example, I can get http://www.xxx.com/forum/%20profile.php instead of normal profile.php page.

Hello,

please open a support ticket with exact URLs so that we can reproduce the issue.