My money is on a bent valve. If you have enough fluid in the cylinder and try to turn the engine and compress the fluid, if the valves try to open at the same time there can be so much pressure that there literally isn't anywhere for things to go, resulting in excess pressure on the valve stem, usually causing it to bend. If it was broken, you'd hear bits of valve grinding away in your engine, usually.
If it's flooded really bad, you can often put the bike in 6th and push it backwards to try to blow things out. Due to valve overlap and rotational speed, this is often more effective than using the starter if things are really bad.
2005.5 KTM 950 Adventure and 2012 KTM 200 XC-W
1991 BMW 318is turbo track car
1989 Chevrolet Caprice Classic Wagon sleeper tow car
1992 Subaru SVX daily
3 Months Exploring the US on a 950