Nibbler's new "game"

First of, let me mention Nibbler is completely fearless. She runs up to
investigate scary new sounds, like the vacuum, instead of running away
or hiding. Up until a couple of days ago, I'd never seen or heard her
thump once.

There is a bunny gate in my apartment she knows she's not allowed to
jump over - my living room is pretty much bunny-proofed, but it just has
too much electricical equipment for me to feel it's totally bunny proof
as yet. Anyway, she's jumped it a few times, I tell her no and put her
back on the other side. Normally, she runs up to it and looks over, and
I say no and she leaves it alone.

The past couple of days she's started jumping over it, but the second
she gets on the other side, she gets scared and thumps and jumps back
over. Today she ran up to it, thumped, and ran away from it without
even peeking over. What's the deal? Does she think this is a game? Is
she enjoying scaring herself? And what's with the thumping? It's not
like I beat her when she goes over, I just put her back on the correct
side... Is she really scared of the living room? If so, why does she
jump the fence? This just seems like very contradictory behavior to me...