Of course, it would make sense that Glen lost most of the magic abilities he had as Frog. Being Frog, he was a magical, cursed, being. Curses can have this effect (like when Athena damned the wise Tiresias, who happened to see her naked: she blinded him, but this also opened his mind eye, allowing him to see the future), and probably magic stats of Frog were boosted up by the curse. Once the curse is lifted, the magic stats would return to normal.
What do you think? ^_^