PlayMaker is inconsistent.

[KillerCreeper]

hi.
Maybe you make a scene with some standard object, with the same setup and see if the issue is still there.
if so you can share the scene here, so i can have a look as well

Here it is. Press F while hovering over an item with your cursor. Then try swapping items and look at the Item variable on the InvSlot prefabs in the inspector.

[Alex Chouls]

Thanks for the test scene. I’ll take a look...