I encountered this bug just now as well:
System: Mac book Air, El Capitan
Steps to recreate: close the variable window (whether you made a new variable or not) -> Spriter crashes
Workaround: I disabled OpenGL from the view menu. No longer crashes when closing the variable window (but now no openGL )
Update: disabling openGL didn't fix anything. It still crashes, just not every time (I was able to make a var once, but then upon making a second var it breaks after closing the window.)