If the ignition is out of time it could fire after TDC, hard on your hand...If it's way too far advanced on the static timing the electronic retard won't go far enough, so you get a kick when starting...a properly timed engine can be started with one finger without fear of kickback....
And TIGHT is the operative word...If the 6 bolts are bottomed out in the hub they feel tight, but the prop isn't, and the bolts shear....Been there, wrecked a 30-10 prop in about 2 seconds and sheared off the bolts..
The direction of rotation tends to keep a single bolt tight when the engine is running, so unless the engine starts running backwards the prop stays on when the 2 anti rotation pins shear....
This is why I like single bolt hubs, or 6 bolt hubs with a big single bolt in the middle...
Our race engine did this, the 1/4-20 anti rotation bolts sheared, the 3/8-24 center bolt kept the prop on....