Godot 2.1
I have many times encountered writing a function, in the case I am currently doing - connecting a function through signal connection, and the function isn't working, so I write a print statement to see if it's called, and upon doing that the function works.
In the current case it's a label being added upon mouse enter, simple enough, added as child to a spatial. It doesn't add it unless the first line is a print statement.
Hopefully I haven't asked this already
