Hover over the favourite button, and you see the following text (Spelling mistakes amended ;) )
"This is a favourite question (click again to undo)"
This implies that you have made the question a favourite already, and clicking will undo it. But the text is the same regardless of if you have made it a favourite or not.
I came across a question that I set, and saw that it had a favourite count. When I hovered and read the text, I clicked again to undo, not realising I had done that to my own question. Of course this just increased the count as the first favourite was from someone else.
Can we amend the text to make it context insensitive? Something like: "Click to toggle this question as a favourite" or "click to set/unset this question as a favourite"