i have a solution for ya - something i figured out a couple of months ago. it is something i have to do on my mac book pro to get maschine to work in midi mode:
drum roll...
0. turn maschine on to midi mode, shift > control
1. go to your mac audio midi setup
2. go to window > show midi window (if you are still on leopard or earlier, midi will be a tab)
3. go to the configuration drop down and make a new one, i called mine maschine, but the name doesn't matter.
4. switch from one config to a diff config and all your midi devices get refreshed, and midi mode now works perfectly!
5. ?
6. Profit!
let me know if that works for you dudes who are having trouble getting maschine into midi mode.