Clutch issue or powerband???

[dbtmpx101]

Hi, I'm new to the forum. Recently brought an 06 GZ250 for the girlfriend to learn on. Long story short, after riding two up on the bike, her practicing for an hour, (hour and a half max,) then riding two up back home (only a mile or so each way) the bike seemed to slingshot forward when I took off. I'm used to my big bike being able to tote two of us around and the GZ being the not so powerful machine it is I did wind it up and take off with liberal throttle usage. Now I find that the bike seems to take off fine but flattens out so-to-speak and then power comes back out of nowhere and it starts pulling "hard". Can anyone tell me if this is how the GZ acts normally or you think the clutch is slipping and after I'm accelerating and feels like I should shift, I stay on it and the bike really starts to move when in all actuality the clutch is just catching up to the motor? Sounds like the rpm's are matched with acceleration but like I said I thought it was weird that it seems to have that rubber band effect.