I've been running into the same "mystery".
I've been doing some extensive revision on my old yard recently.  From what I can tell, when I do something to existing switches, the crashes happen.  I am noticing also, that it seems to only happen to the switches that were IMPORTED from 2006 . . . specially when "rotating" or "replacing" the switches.
But, it seems to never (I think never, I may be wrong) happen to the switches that were "newly created" in 2009.  
I have been replacing and adding switches in an "old" area.  YOU WILL get an indication that its getting ready to crash.  As soon as you "replace", "rotate" or "move" a switch, BOTH arrows will turn RED.  SAVE immediately then EXIT surveyor.  8 out of 10 times, as you exit surveyor,  it will crash.
Re-start and re-open the surveyor with the same route.  The switch should show up with the proper "green/red" arrow.
BUT. . . if this happens a few times . . . you will get a prompt for a "broken database".  Then click OK . . . LAUNCH Trainz . . .  CLICK ASSET . . . CMP will launch and AT THE BOTTOM Windows Task Bar will display "Repairing Database".  Let it finish repairing then re-start Trainz.  Just yesterday, while revising my old yard, I had to to do a "Repair Database" about a dozen times in a 4 hour period.  What a hassel !
I can't wait for this problem to be fixed.  SOON I hope.  But in the mean time . . .  this is what works for me.
