>>. You add a -king (frolicking, panicking); ditto for -ed which somehow becomes -ked. Why not frolicing, panicing? That would be more in the tradition of the language: yet another exception to remember.

That practice began after the Norman conquest when people were confusing Germanic C (K) with the French version (S)
So the present particle for prance is prancing, and for picnic it's picnicking - although I suspect the K will someday be elided.