Avoid that High side ride....

[Jayock]

you may have an underlying issue here. typically you should brake using both front and rear. now i will use my rear brake alone when trimming speed in a corner when i get a bit too hot, but other than that i only use the rear in conjunction with the front. if you lock up the rear you will start sliding ect, but it sounds as though you are locking it up very easily, i would start by checking my brakes to see if they are grabbing for some reason, adjust brake lever if its too high, and also check your suspension, if someone did something like tighten your preload a lot more than you need your back end will be in a "ass up" position, which makes for easy turn ins but causes your rear end to be essentially "light"

I suspect you will lose the habit of using both brakes after you are racing for a bit.