Foot sliding forward in boot..??

I am just geting consistent and landing in the flats on HS jumps... butt down, progressive edge, rope in and stand tall... it is amazing how you float!! And this is with an I/O.. I can't imagine a BIG wake. Anyhow... it is getting annoying that when I land, my front foot is sliding forward in my boot. Each time I land far, my foot inces forward a little more. And I can't wiggle it back. I have '05 LF Alpha's size large. My foot is a 9.5 to 10. I tighten them up as tight as possible, but I can't get my foot to stop moving forward in the binding. The only way I can get my foot back is to drop and then loosen, move my foot, and retighten the binding. I don't use any lube to get in them. Is it me or what gives? Same thing happend with a set of old HL Spin bindings I had, but those wouldn't tighten up very tight and I thought that was the issue. But now, I am wondering if it is me!!