I was experimenting with using a Number2 object (stop your snickering) as a way to make a dynamic receive for floats and ran into what is probably a bug. The idea is that you can set the receive name dynamically like this:
This is all fine in the top-level of a patch, but if it's in an abstraction, then it sometimes generates one of those pink highlighted error messages in the parent window and then things are broken.
The problem happens when the receive name property of the Number2 object is empty. So just assign some placeholder receive name, save the abstraction, and you're good to go.