Never had that happen to me in over 35 years of riding bikes. I do go over the handlebars occasionally. I have had the front wheel slide from under me a few times as well (my least favorite way of falling). I even ride with a low tread back tyre so I can slide the back wheel around a bit on trails.

Maybe you instinctively apply appropriate pressure using the front brake.

If you slam on the rear brake only or simply much harder than the front brake, the rear wheel locks up before coming to a stop. The bike will continue forward with the front wheel rolling and the rear wheel sliding. If there's slight braking on the front wheel, the rear starts sliding around the front, twisting the cyclist.

Fishtails are pretty easy to control though. Going over the handlebars, not so much. (though that requires a lot more braking power, to be fair)