Or, it's gremlins.
I had a plane that would surge out of the corners. Bad. Did it for 10 or 12 flights while I tried the usual stuff. I took it apart, pulled the back off the tank and cleaned it, cleaned the NVA...again, changed fuel filters and fuel line. I figured that if that didn't do it, I'd go to a new tank or something. The thing flew fine after that. For many, many flights. I didn't really do anything, but it sort of fixed itself. I suppose there could have been an undetected hole in the tank that was fixed when I put the back of the tank back on, but who knows.
I went with the theory that I had trapped a gremlin in the tank and taking the back off let him out.