When your WPF menu alignment is wrong
I had a very weird problem where my menus on a WPF application were dropping down to the left instead of the normal to the right.
It turns out it is due to having a tablet setting set to right handed ... even though I don't have a tablet. The answer was found on the link at the bottom of this post.
To fix it:
Press the Windows key + R and then copy/paste the following line of text.
In the Tablet PC Settings configuration dialog select the "Other" Tab. In the Handedness section, place a check mark in the Left Handed option.