2013 Te310 Stalling Downhill While Gearing Down

I'm stumped. Bought a '13 te310 for the girl. Beyond the starter issue and this stalling/locking up, it's a damned fine bike, but she's going to die.
Just sorta coasting down a rather long steep hill (street), she gears down to get a little engine braking, lets out clutch, and apparently the bike just stalls and completely locks up. It starts right back up every time. I'm trying to wrap my head around what the hell could possibly be going on here, and suspect it's probably a common issue that I'm just not finding the correct search terms for?
I keep thinking that somehow the negative torque is maybe causing the starter sprag to get jammed forward and into the locked position somehow... Locked hard enough it doesn't release perhaps? But that doesn't really make sense because it starts right back up without any issue.
Idea's?

hi,
i had the same problem but mine is when the bike is hot or cold not in the middle of temperature, i had try to change the water temperature sensor, i make a shim of the valves clearances with a little better performance but not solve the problem.
On the forum also i read that the ADC (automatic decompresor, im not sure of the name) may cause problem in this bike or maybe a flash of the ECU but the last owner didnt touch it.
i will try a new inyector (that can buy and return to motocrosscenter)and comment if it solve that frustating problem.

sorry for my english .