Did a quick sketch over the png file, ghost Willy is in a different pose
but facing left and in that area, magenta line is roughly where ghost Willy is
standing and where I've seen live Willy go splat a few times.
The test file is bigger than the one I've been running (1.05 vs. 1.06?),
but I've downloaded it, will see if it shows up again (tried twice just now, first
three levels once through with each version, ghost Willy didn't show up, but did
manage to hit a phantom platform once, although the position seemed to be a
fully erased part of the collapsing platform below).