http://mantis.team-mediaportal.com/ is the bug tracker which is the place to search before posting bugs.
The elite-squad link will direct you to the test team forums where you can report bugs - there's also a tool you can run that will gather information about your system plus mediaportal logs so that it can be attached to the bug report.
If you pick one of the forum topics for bug reports at the test team forums it will contain a sticky thread giving a link to the test tool.
Bugs don't get put into Mantis until they're confirmed by other testers.
Thanks