SSRS - Report Parameter Format issue

This issue may be cause by the language of the Operating System and Web Broswer. Please try to change the language of them and check if this issue is persists or not. Here has a thread which is similar to yours, please see:

http://social.msdn.microsoft.com/Forums/en-US/sqlreportingservices/thread/32b62d3c-9a32-41bd-b7ad-95c3b89a7668=0,false,true)