Hello,
this behavior is at the moment–unfortunately-expected behavior. Cubasis does not forward the MIDI that it receives to the output (MIDI Thru). Thus, you would have to record your MIDI events and play them back to be able to control external apps or hardware.
The good news: We have this feature on our list and plan to tackle it soon.
The issue with Cubasis and Sample Tank is indeed unrelated with the problems that you experience with your keyboard.
Kind regards,
Frieder