Using sample in Quad Engine with exernal MIDI Keyboard

This is normal behavior. 1 MIDI note means it triggers 1 voice.

Because you have enabled all four pulses? Or what do you mean here?

Currently not. On quad engine, if you trigger a note with the internal or MIDI keyboard it plays the pulse (and corresponding mini engine) that is selected with the X encoder.

The (temporary) solution for this is:

(and setting polyphony high enough)