This has happened on my shee, acouple of times and it is scary as hell..
Before I had my complete motor rebuilt this happened, did a leak down test and nothing, so I cleaned the carbs and forgot about it..
I had my motor done, top and bottom, everything new, gaskets, seal, everything, It happened to me again and this time the bike through me on my ass so fast i didnt even kno what happened, luckily I was wearing my kill switch and nothing happened to the shee...
I was told that this is caused when moisture or some sort gets inside the carb...
Was it real cold when this happened to you, did you go through water or something?