Someone on my yard was watching me jump and said that the only equine she has ever seen do that before was a shettie. TBH I reckon D is part shettie. She's also the only equine that has ever pulled me off my feet other than an evil ginger shettie that escaped from the locl pub beer garden.
i thought that they give you a few seconds (perhaps 5 or 10) and then if you have stopped for this length of time then they count it as a stop. i only know this as i used to ride a napper and sometimes he's nap nowhere near a fence and i've got away with no faults before and had faults if its gone on a little longer. also...if you horse stops for a poo before you jump the first fence and after they've rung the bell you can put your hand up and ask them to stop the bell...
I'd think as long as you don't cross tracks or step back, you'll be fine! Murph doesn't eat going round, but as soon as we jump the last jump and I relax contact, its like someone's turned the power off and he goes canter to walk in one step, then down goes his head. 'Tis a tad embarassing sometimes, I must say.