F5 runs highlighted text, not current file.

When I'm editing a Python file and accidentally highlight one or more characters then hit F5, script attempts to run the text I've highlighted. Instead of the current file, I'm running, say, a half-line of code, or even just a new line.

This is slowly killing my will to live. I can't see where this would be used, ever. If it is actually a Thing that people want, please put a toggle on it so I can turn it off. Thanking you in advance.