I too had a grass carp bite a top water, jitterbug in my case.
Here is how the story went:
I was fishing a small creek near Ottawa out of my canoe with my GF. We had paddled to the first riffle and I noticed what looked like a musky in the shallow spot before the riffle. When we got close, I confirmed it was a musky. I am not sure how it got there but it was there eating all the creek chubs it wanted. My only thought was it either came down the Fox or it escaped a pond upstream and made it to this creek. After getting too close ( more like almost on top of it), it took off downstream. I decided to make sure and fish all the way back to the truck with a jitterbug in hopes of hooking the big boy. I estimated it around 30 inches. After hooking a 12 inch smallmouth, I made a long cast to an eddy and out of the blue a huge surface busting attack took place. I set the hook and felt the big fish on the other end. I shouted " I got him"!!!!!!! "Baby, I got his (beep)". " How lucky is that"?
After a few minutes and gaining ground, I caught a glimpse of this brute. My eyes could not have been any wider when I realized I didn't hook the musky but rather a 9 or so pound Grass carp. I laughed it off while I worked the fish till I could step out of the canoe and unhook him.
My only conclusion to this rare top water carp bite was a case of mistaken identity. I had never in my years of fishing the local waters seen a carp bite the way it did.