I've not been erroneously charged either. I did contact FasTrack when I first transferred my transponder to the Tesla, and they acknowledged a problem with Tesla and put it on some manual list as it was described. It's set to 3 in the slight chance the signal is picked up, but I've not had to haggle over inappropriate fees at all......and I've been up/down the state across multiple tolling jurisdictions.
This is how the guy described it to me.........When the FastTrak camera picks-up your plate without a corresponding transponder signal, it triggers a fee to your account (or soon by mail plus a penalty if you have no account at all) because the system is programmed to the rules "transponder must be with the car", (not at home, in another car etc.). Unless you are manually placed on the exception "list", it's is not auto-cross checked with any other allowable scenario. It's simply, you were in the HOV with no transponder present so KA-Ching.
FastTrak currently does not know or police every HOV sticker which is issued by DMV. They know only because we tell them but it's the make/model in their system which triggers an exemption to those EV free tollways while charging us for all others. (HOV stickers allow us in all HOV lanes but not all HOV lanes are free to us) The physical stickers matter only to CHP, because short of knowing every exempted make/model, they can't monitor non carpoolers in the HOV lane. The DMV also cares as its a source of $24 plus all the fines issued by CHP for not having stickers.
FastTrak is an independently contracted company missioned now with collecting tolls only. Try calling them separate from a mischarge and ask if there is a better way to handle this. Its a real shame if you have to do this weekly.
This messy execution is why CA needs to replace the entire HOV mechanism with either exempted EV plates or improved technology.