What Is The Design Characteristic That Causes A Cap To Snap
Tip stall, snap roll, spin: they all cause rotation because one wing stalls. All you have to do is increase the angle of attack to the point of stalling. That can happen at ANY speed. Too much elevator can cause the plane to reach that critical angle easier, that's all.
You can do a basic test to see if the plane is "rigged" correctly (i.e. any difference in symmetry, wing warpage, etc.) by doing a straight ahead power off stall. Try and maintain level flight (no rolling) with RUDDER only. When the plane stalls, it should tend to fall off straight ahead. If not, it can help point out which wing may have a problem (might be an asymetrical horizontal stab, too). If you use aileron to maintain level flight (in the roll axis), you will aggravate any yaw tendicies because aileron's CAUSE yaw (it's called "adverse yaw").
As others have written - keep your speed up and watch your elevator input.