My wisteria did the exact same thing! The original bunch I planted in the tank a few weeks ago was very dark green and fine leaved. Since planting it has sprouted all new growth as bright green, fat lobed leaves. The bunches of new leaves have "pupped" off and are floating in the corner of the tank. They each have a root system dangling down; it looks like a group of water lettuce floating in the tank. I took one of the pups and planted it in the gravel. It is growing, but in the big leaf form.
90 gal Tank is as follows: Temp 80-82 degrees, pressurized CO2, lighting- (3) 48" ODNO & (2) 48" NO. Dose with flourish & iron once a week or with water changes.
Any further suggestions whether this transfomation is good or bad? I've been very curious.