I tried to reconstruct the environment I had offline.
With WP Hide Dashboard and Profile Builder. I installed them both and got the same result.
As you said I get it even when I only hit Login Button.
I changed the blog URL from the install directory. With the index.php and .htaccess . Can it come from there?
Next is that I added the WP Login Box to the header. But I also tested the plugin and shortcode (both brought up the same problem)
I'd have another idea. Maybe some Permission issues with the configs, although your plugin didn't give me an error when i changed something. I have no FULL Write Permission (Changed nothing and had to write my own .htaccess file and upload it per ftp)
So now that's all I got with my "skills" :D
Thanks anyway, hope my ideas and circumstances could help bringing you to the solution.
Greetz from Germany, Lars
EDIT: I got WordPress 3.5.1 offline and 3.5.2 online
2nd EDIT: Just updated the offline version to 3.5.2 and your plugin is still working