The mantis site has been taken down. The existing data has been saved.
None of the active developers were using it anyway.
If we want to use an issue tracker (potentially a good thing) I'd suggest using the assembla ticket system or the ticket system in the assembla trac. If neither of those are suitable, there are various other hosted ones we could probably use.
In the meantime, all issues should be reported in the forum. This is a good way to sort the actual bugs from the support issues anyway.