using multiple MIDI inputs

[v.muller]

I would like to make a "travel" version of the arrangement keyboard.
I have these two short keyboards: CME Xkey 25 and CME Xkey 37.

I would like to use the 25 key version to play chords with my left hand,
and I would like to use the 37-key version for playing melodies with my right hand.
The problem is that if I select Xkey 25 as MIDI 1 and Xkey 37 as MIDI 2, I can play chords with my left hand, but my right keyboard doesn't produce a sound, even if I check "play notes." MIDI 3 and MIDI 4 also don't work; only the MIDI icon flashes.

Am I doing something wrong?
Should I set anything else?