When you say the toe strap is coming loose, do you mean it's sliding off your toes? Make sure it's centered on the front of the boot when tightened down, not off to one side a bit, its a common mistake people make. You may need to move the adjuster screw into a different hole on the strap to get it to line up with your boot. With cap straps you can move them so they are directly over your toes or kinda inbetween the front of the boot and over the toes (optimal in my opinion) If you can move it with your hand it's too loose.
If the tightness itself is loosening, you may have stripped out ladders (the plastic part that your ratchets connect to.) Do you hear a pop sound sometimes where buttering? Check the teeth for wear. If the ladders look worn, and they are only a year or 2 old, contact Burton Rider Services and they will hook you up with new ones.
Either way it's an easy fix.