This one may be difficult to track down.  It's literally the only time I can remember experiencing IQ crashing in the last year, and it's totally random, and happens a minority of  the time I do it.  Tools > Field Properties.  I then often resize the field properties window to a different size, so I can be looking at something else in IQ as I am making changes to a field.  As I'm resizing the field properties window, IQ (on occasion) crashes.  I am 90% certain I've had it happen on both computers I run IQ on.

 

Low priority but since crashes are never fun, and as a rule IQ otherwise never crashes, I figured I'd report it.