I also had this problem of exporting a part of an existing MIDi track by using drag and drop to a Windows folder - in my case, I normally get as result the whole MIDI track exported as a MIDI file, despite of initially selecting only a part of the MIDI track. I solve this by applying trimming before exporting (select the needed clip, doing Clips --> Apply Trimming, then exporting). This is to avoid the (otherwise nice Sonar feature of) slip - editing. 

This is a very old thread but some thigs don't change.
 
It's as simple as this: 
File 
"SAVE AS"
"MIDI 1" 
I do this a lot. Even a complicated muti track audio and midi project using 10 VST instruments and a zillion plug in effects will be saved. 
If you then open this file even in a different DAW all the fancy stuff and audio tracks will be gone but each midi track will be there and still maintain it's original channel. 
If you want the midi file to be GM compatible you will need to set the tracks up with their own channels etc. You would also need to use GM patch and Bank assignments. Best to open this file with TTS-1 as the only VST to check how it plays. 
 
If all you want is one track , say the drum track, then myself I do the same but I re-open the midi file in a new project and simply delete all the unwanted tracks, takes 2 seconds. 
 
Another way I would do this is make a back up copy of the original project and then delete all but the midi tracks I want saved and then "save as" MIDI 0 " this will take a bunch of drum tracks and clips and make it into one nice track.