@Cyberdevil is right there's something funky going on with the Triple the Power medal. Same exact thing happened to me first time through the game -- that medal didn't unlock but all the other medals did.
Started afresh and was able to get that medal the second time through. I think I know what the problem is and it is due to game bugs but if you had problems getting that medal and want to get it, ...
Step 1) Clear your browser cache *or* start a game on another browser which does *not* use the same "flavor" of Flash, so in other words if you did it on Firefox, now do it on Chrome or if you did it on Chrome, now do it on Firefox, as one example.
Step 2) Generally try to avoid everything (as much as possible) except those P items.
Step 3) Before taking a P item make absolutely 100% sure you are *NOT* invincible and/or temporarily hit. Very Important! Also don't take *any* jetpacks
Step 4) Only if you meet the above, now take the P item and wait for it to completely wear out. Do *not* take additional P items while a P item is still active. Very Important!
Step 5) Repeat the above thrice and most likely this time through you will obtain the medal and be done with it.