Hmm... on subsequent attempts, I didn't get a crash. Weird.
Here's something to try out:
Test 1: After splitting the notes to tracks, go through and change the output instrument on the split tracks to AD2 if it's not already (if it is, change it to something else, and then change it back to AD2). Any crash?
Test 2: When splitting, when the dialog box asks for what port you want, change that to whatever AD2 is - should be at least Port 1. Any crash?
I'll keep trying a few things out. It's possible that this is somehow not triggering unless SONAR is opened cold and the project is loaded right away - I did all of my tests by just closing the project rather than SONAR entirely and starting fresh.
EDIT: Nope, can't get it to crash again, no matter what I do, even on a fresh start. Very odd!