I had a false positive once when my Nikon 35mm was scanned. I did not get felt up but did get ID/ticket verified and EVERYTHING in my camera bag swabbed. The TSA supervisor asked questions about where the gear had been but never made any accusations or assertions about anything. They offered no explanation for why the event happened other than "these things sometime happen". The TSA handled my camera gear very carefully and asked when they weren't sure. They insisted on re-packing my bag and did so EXACTLY in accrordance with my direction. The total delay for all of this was 15 minutes. I found the event to be a very minor inconvenience, at most.