Midi Playback Problem w/ Multiple Tracks

Midi Playback Problem w/ Multiple Tracks

I am a new N-Track user and am trying to get started. My objective is to import 3 separate midi tracks I have written, then, add vocal, and live guitar via MIC in N-Track, and mix down to CD.

I have imported separate 3 Midi Tracks for Violin, Viloa, and cello recspecively. I did some editing on each using Piana roll.

My problem is, on play back, not all the midi notes are played. It seems that, sometimes, when the separate tracks share the same note, only 1 track is played when that note is played.