.. it is an idea.
You check if you have set some interface object in some "placeholder for item". In this case, the object may go in that area.
I'm not sure I follow exactly, but the placeholders are completely plain. No values, no conditions, no command groups, nothing. As the game is in early development (as you'll notice from the screenshot), I haven't even tried adding anything fancy.
As I also stated, the weird thing is that if I build the game to an exe, then everything works fine. This seems to be a player/editor issue for me.