Exactly how are you putting weight on your front end? You should be scooching your butt up to the tip of your seat and leaning over your handlebar. Stay loose and don't stop pedaling. There might be something I missed in there, but the rest comes with practice. It's nothing like road biking, unless you're on pavement.

Oh yeah, and just to be sure, your only problem is keeping the front wheel down? No traction issues?