Yesterday I was out flying Acro with my instructor and allegedly we violated Class B airspace.

We were doing three series sequences at 3000 and the Class B floor where we were was at 4000. The seqeunce consisted of a "Sharks Tooth" to an "Immelman" followed by a "Spin".

Upon completion of the Sharks Tooth I began to setup for the Immelman. I started the brisk pull-up and noticed a jet flying above me at a distance of approximately 1000-1500 ft away. After completing the manuever, I glanced back to my 6-7 O'clock and saw the jet pass by at an altitude still slightly above us. This is key, because I am 99% certain the jet (later on learned it was a G4) was above me. We proceeded back home and after calling regional approach we are given a phone number and instructed to call once back on the ground.

My instructor, who by the way is an airshow veteran and has over 24,000 hours under his belt was also certain that we were not above the jet.

We headed over to a local restaurant and called the number. I initially spoke with the controller. Apparently the jet had called us in and and he was flying at 4000ft. The controller said that the jet's TCAS reported us exactly at 4000 and so did the controllers mode C. I tried to explain to the controller that we were certainly beneath the jet and given the performance of our aircraft (8KCAB Super Decathlon) it would not have been possible for us to be above him given the manuveurs were doing and given our entry altitudes. I handed the phone over to my instructor and he discussed with the controller for about 10 minutes. The controller got all my information and said that I would be receiving a call or a letter in the near future.

I am really concerned about the whole situation and am wondering what the consequences of this incident could be. Given that I was receiving dual at the time, who is liable? Also, I truly have a very hard time believing that we were at 4000. However given that he reported us at 4000 and not 4100 or above, technically if we were in class B, then we would have only violated it by 1ft. This is obviously a very fine line and there must be some slight discrepancies in the accuracy of Mode C altitude encoding capability.

I am not one who does not respect the rules of the FAA and am cognizant of the importance of Class B and the lives put in jeopardy if class B airspace is violated. If I would have been flying the manuveurs on my own, there is no way I would have felt comfortable flying beneath the class B shelf and normally if I am without my instructor I head out much farther where I have more room to execute the manuveurs. However, given that I was instructed to fly the manuveurs there and given that I relied upon his experience and knowledge, I felt comfortable.

Anyone with any experience in such a situation? What could realistically happen? What could the worst case scenario be? Am I a liable or is my flight instructor liable?