Another thought. You say you're going wide open when this happens (or maybe someone else said that) - but how high are your rpms when you punch it. If they're too low to start with in a given gear then the engine will chug a little to get moving and once it does get closer to the powerband (and over the point of lowest optimal RPM in that gear) it'll get easier for the motor to push and it'll take off. RPM doesn't drop, but the engine doesn't have to work as hard to gain speed.
To me this is likely what's going on, and it's not a problem. You'd be better off to use a little more of your rpms if this is the case, though, these little engines like more revs. You don't have to run it at redline all the time, but don't go driving it like a Camry, either.