The editor spawns you actor twice. Once on drag to create a preview actor, and then again (the actual actor) when you release the mouse. Based on my humble knowledge there is no way arround this without a huge engine mod for a very minor thing. There is however a workarround. Put everything you don’t want for giggles on the PreviewActor in an “if”.
{ MyGiggles(); if (!HasAnyFlags(RF_Transient)) { MySh…tuff(); } } in the OnConstruction(Ftransform& … stuff) that is,… on your actor.