Whilst wandering level 7-4 as Simon, I tossed a cross/boomerang behind me (to the left) and allowed it to fly slowly rightward as I advanced through the level. Eventually, the boomerang vanished mid-screen but I could still hear the boomerang sound. I had the [II] powerup so should have been able to throw 2 boomerangs yet, after this occurred, I could only throw one. I think the system thought the boomerang was still flying, even though it had vanished.
At first I thought you were talking about Link. You should say Cross/Cross boomerang for Simon so we know which character we're talking about.