Vortex Sound Research

Hi everyone. I have a Behringer Crave and a Make Noise 0-Coast and want to control them via MIDI. Both have their own MIDI channel and play separate melodies simultaneously. The MIDI signal goes from the audio interface into the Crave and from the Crave into 0-Coast. Everything works, but if both synths play the same note at the same time (i.e. both play C3) only the output from Crave will be heared. Is this normal? ?

When both play different notes simultaneously, both synths make sound as expected.