- What browsers show this problem?
Answer: I'm using Google Chrome. I don't have any other browsers though, so I can't test it on other browsers. - Please share an example project (if possible).
Answer: - Describes the steps to reproduce this issue.
Answer: Open a project on the Snap website, run it, and then try to scroll down. - What does Snap! currently do?
Answer: Refuse to scroll down. Keeps scrolling back up again and I have to double-click outside the project for it to work. - What should Snap! do instead?
Answer: Work properly.
I'm also using a laptop touchpad to scroll down, if that helps.
By default, on a project page, the project has the focus. That's because when you open a project you want the keyboard and mouse to automatically work in the project without having to click on it.
If you want to scroll the page you should, well, click on the page 
I'm afraid there's no way to detect what a user intends to do, so we need to decide on a default behavior, and having the focus inside the Snap! project is the one most users are going to need.