I had this same issue initially when using that variation. The first and foremost solution is to get rid of Kreeping Ice...it's pretty ineffective anyway. BUT, if you've found a way to make it useful don't listen to my input on that.

If you have Kreeping Ice equipped, you need to input a deliberate delay before hitting the button in the combo. So, do the motion of F, D,F, Wait, 4. The wait should'nt be more than one second in length, but it WILL work each time. Jump into fatality practice and try it out a few times...you'll get the hang of it quickly.