I must say it is unusual for just moving blocks to cause a crash (I haven't encountered that), but I will try out your scene to see if I can reproduce this. Is it processing MIDI messages at the same time?
However, I have fixed many crashes in the forthcoming version of MidiFire and it would probably be an idea for you to try that out on the beta, once that is ready. If you're not already on the beta team and would like to do this, just PM me the email address I should use with Apple's TestFlight (your Apple ID) and I will add you in when the time comes.
There were certainly some messages coming into MidiFire while I was editing, although I wasn't actually playing anything.
I had two keyboards connected via a MIDI solutions merger (old version) to the Korg plugKey.
On channel 1: Yamaha KX88 which sends active sensing.(In MF setup Ignore active sensing is set to yes.)
On channel 2: M-Audio KeyStation 49e which has a dodgy volume fader which sometimes outputs control changes without actually being moved.
These messages are blocked within the scene in the example I sent, but in some scenes where the problem occurred the channel 2 fader was used.
The plugKey is also a suspect. It occasionally seems to repeat notes when I'm playing busy piano parts. (For that reason I've given up on it for live use and gone back to the iRig MIDI, and I very much appreciate MidiFire's ability to transparently change between them.)
MidiDesigner Pro2 and the BlueBoard (with one volume pedal connected) were also active, but I've never noticed spurious messages from those sources.
Thanks for the offer of the beta version, but I don't expect to be doing a lot of work in MF for the rest of this year and I probably won't have time for any detailed testing.