Why am I only seeing a few modules in the Multi Select Lookup Properties popup?

Why am I only seeing a few modules in the Multi Select Lookup Properties popup?


When I use a Lookup in my module, I can see all my modules in the Lookup Properties popup. But when I try to use a Multi-Select Lookup, I only see a few modules in the Multi Select Lookup Properties popup.

Why would this be? I cant use the module that I want to!

Thanks