Windows 7 32-bit with IE9.

I'm unsure if this does the same thing under phpBB, but it does here at .com.

Start or reply to a topic. Click the bold BBCode. The cursor is placed inbetween the opening and closing BBCode tag. Now click the underline (or italics or other formatting BBCode). The cursor is placed after the [/b - rendering invalide BBCode usage.

Clicking compatibility view fixes this.