Dynafit Bindings are fustrating.

I've had the same problem. If there's any doubt, clean beneath the toe piece.

Another test: LOCK the toe piece after stepping into it. If it's exceptionally difficult to lock, then you have the problem. Remove your ski and remove the ice. If it's easy to lock, then return to normal release mode. It's usually more difficult to get the toe piece to initially engage when the ice is present, too.

YOU MEAN DYNAFITS AREN'T LIKE NORMAL DOWNHILL BINDINGS!? THE HORROR!!!

Like Tim suggested, when things get packed up with ice, I hold my skis vertically or sometimes upside down and cycle the toe-piece until all the ice falls out. After clicking in at the toe, I lift the ski to be sure that the pincers are in the divots, then slide the ski forward and back a couple of times to be sure that the cutter slots have done their work. I then make a quick visual check that everything is fully engaged, stomp the heel, and head off for nirvana. Takes five seconds, once the ice is out of the toe-piece recess.

Sky's suggestion about locking/unlocking the toepiece has also worked for me.

I probably don't ski as hard as you do, Scotsman, but I've never experienced the pre-release as you describe.

Watch out Scotsman, start bad mouthing Dynafits and pretty soon your cats start disappearing, "Fritschis suck" gets spray painted on your garage door, and your kid gets beat up at school.

Has anyone tried spraying teflon or some other lubricant in there in an attempt to prevent ice build up? If nothing else, it may make that area easier to clean. I have found TriFlow to be a miracle substance in this regard.

...speak of the devil, my new Vertical ST's just arrived in the mail, yippee!

A friend of mine has had similar issues recently, with no ice/snow build-up evident in the toe piece.  When playing around with them on the bench, you can see that the pins would engage the toe of the boot, but the spring levers in the toe piece hadn't fully flipped down, but were hung up right in the middle.  It was enough to support the ski when lifted, but would typically pop out almost immediately.  She's started rolling the toe up, sliding the ski back and forth a couple of times and pressing down on the toe when the heel is off the deck to get the levers to flip the rest of the way down.  A little silicone spray has helped somewhat.  She can also seat them by hand, just by pressing on the pins -- it doesn't take much pressure at that point.

Not sure if that's the same problem, but there you go.  Might be worth a look.  Are you using your NTN boots here?  Could that be part of the problem?  I can't remember whether you have Scarpas or Crispis, but Scarpa has made some design adjustments to the Dynafit toe fittings for next year's model.

LOCK the toe piece after stepping into it.

If you can't get your normal, say, 4 clicks, it may indicate a problem.  Chris, are you just picking the ski up in place to see if the toe will support the weight of your ski? I was suggesting actively sliding the ski back and forth (say 2 feet back) before stepping into the heel.

Yea Greg, I am lifting the ski and moving it back and fro.
I guess the lesson is that with Dynafits, you have to take extra time to ensue the binding is properly engaged before launching. 

It was a bit of an eye-opener though yesterday when I discovered that even with the ski hang from toe pincers test, you can't be sure the binding is properly in. I think I will always check for ice under toe piece before dropping in on steep terrain henceforce. The silicon spray is a good idea as well. Thanks for all the good advise.

I realize I have risked the wrath to speak negatively of one those two TAY sacred cows " DYNAFIT BINDINGS and SUBARU'S"