MySite A potentially dangerous Request.Path value was detected from the client

I got an issue with some redirections on my mysite. We got usernames with white spaces in it, so mysite url is like this http://servername/personal/firstname%20lastname/

So when I open the Settings page for "My Tasks" the following url is generated for the "Save" button:

http://SERVERNAME:8080/personal/FIRSTNAME%20LASTNAME/Settings.aspx?source=http%3a%2f%2fSERVERNAME%3a8080%2fpersonal%2fFIRSTNAME%2520LASTNAME%2fAllTasks.aspx

As you can see the original "firstname%20lastname" has been escaped again in the source parameter so the result ist firstname%2520lastname which is not a valid url anymore. The percent symbol shouldn't be escaped again. So if I hit Save the following error message occurs:

Sorry, something went wrong 
An unexpected error has occurred. 

Plus this lines in the uls log:

06/05/2013 10:45:31.77 	w3wp.exe (0x2DE0)                       	0x3AA0	SharePoint Foundation         	General                       	8nca	Medium  	Application error when access /personal/firstname%20lastname/AllTasks.aspx, Error=A potentially dangerous Request.Path value was detected from the client (%).   at System.Web.HttpRequest.ValidateInputIfRequiredByConfig()     at System.Web.HttpApplication.PipelineStepManager.ValidateHelper(HttpContext context)	 
06/05/2013 10:45:31.77 	w3wp.exe (0x2DE0)                       	0x3AA0	SharePoint Foundation         	Runtime                       	tkau	Unexpected	System.Web.HttpException: A potentially dangerous Request.Path value was detected from the client (%).    at System.Web.HttpRequest.ValidateInputIfRequiredByConfig()     at System.Web.HttpApplication.PipelineStepManager.ValidateHelper(HttpContext context)	 
06/05/2013 10:45:31.77 	w3wp.exe (0x2DE0)                       	0x3AA0	SharePoint Foundation         	General                       	ajlz0	High    	Getting Error Message for Exception System.Web.HttpException (0x80004005): A potentially dangerous Request.Path value was detected from the client (%).     at System.Web.HttpRequest.ValidateInputIfRequiredByConfig()     at System.Web.HttpApplication.PipelineStepManager.ValidateHelper(HttpContext context)	 

This issue also exists when trying to open /Social/sites.aspx depending from where you try to open the url. I have no clue on where to start, maybe somebody here can give me a hint!