hmm, I've seen this issue before but it has to do with using sef but becuase your using jdiction it could also be causing a conflict, I know with sh404sef you can define the link you want to work, and it should work perfectly using all of the standard joomla setting but I truly believe jdictions is causing he issue and cannot provid support for their component you would need to contact them regarding that , otherwise use a custom sef component
Hi! That is what I think also. I'm already in contact with the jDiction developer.
Many thanx for your thoughts and support. I will reply here again, when I know
the solution. Maybe it can help other users too.