This is happening because of the button chrome built into the default template for the control. Your only workaround is to re-template the Button. This article should get you started.

Why does WPF toggle button pulse once unchecked
Assuming a comment won't fit (or can't go) on the line it applies to, should one write the comment before the code or after?

Well, wherever future readers will best understand the comment's scope. In other words, wherever most programmers/scripters put such comments.

So where do most programmers/scripters put a comment: before or after its code?

If your answer applies only to specific languages, please indicate which.

And if you can cite an accepted spec or guide that supports your answer, so much the better.
