My right click menu is broken.
I use right click constantly to open links in a new tab. Sometimes when I right click, it does a left click and a right click at the same time. I will click a link, and instead of opening in a new tab, it will open in the current window while briefly showing me the right click menu as the new webpage loads.
Are you sure that your mouse isn't causing that?
The only time I have seen something like that happen is when my mouse was on its last legs - the spring for the right-button was weak and ready to fail completely.