To the best of my knowledge, the following by-product
of the use of ^C while computing strong generators for a
permutation group should not occur.
Let G be a permutation group defined by a list of generators,
and let the first function called after the definition of G be Size(G).
I press ^C^D before it finishes, then call Size(G) again. It returns an
answer instantly, since G.size is already defined. Moreover, sometimes
G.size is wrong in this case.
I beleive that G.size should actually be undefined.
At least I don't know of any place in the GAP
manual mentioning such effects.