I thought Kat's performance was wonderful and also preferred it to Mandisa's.
I missed the couch action ... but doubt she was being a poor sport, jealous ... whatever. Maybe she was just reliving her own performance, because after all this is an individual competion.
I think the "wierd" behavior may have just been nervous excitement about her accomplishment.
Her looks and presence actually remind me of someone I know ... pretty and with that earnest, nervous ... exuberance.