Try (as a work around) making a new schematic by copying & pasting all 3 schematics onto one big page. Then check for components still left in the Component bin.
I will try this, but my problem was that the schematic came to me without any unused gates been left in the component bin. I had to delete the component and then re add to the schematic.
As a rule I would place them on the schematic and as a final act tie the inputs.