Ludwig, here are a couple of simple setups you might try to reproduce the long stuck notes:
Send midi from Little Midi Machine to a midi track in Cubasis. Send a sequence of the same note for each step at 120bpm. Adjust the gate length of the note to maximum. Record the sequence. Apparently there is a threshold of note length that causes the note not to cut off. Shorter lengths behave normally.
Here is another test:
Send midi from Arpeggiator Pro to a midi track in Cubasis. Set the midi out of Arp Pro so that the gate time is Manual (in the midi out settings under the gear button). Then on the main controls set the gate time to 200%. Record any arpeggio sequence and you should see long overlapping notes in places.
Hope this helps, if I can answer any questions, I will try. Thanks,