What is happening in PIE isn't happening when I hit "Play"

I have a weird problem. I’m trying to “Cut away” meshes at runtime. It works in Pie (Below) but not when I click “Play”.

In Pie I have this (Meshes are cut away – Good!):

But when I click play I see this (Meshes are not altered – Bad).

Got the idea from here:

Any idea what could be causing this?