Comment 177 for bug 187313

In general, the described behavior happens when I move the mouse while down-clicking and immediately up-clicking (releasing the click). It seems that when I up-click, the mouse is over a transitive drawing of the buttons in the context menu, and the up-click selects a button that I am not intending to select.

Although I would also swear that this happens when I'm fairly certain I do not move the mouse.

Hope this helps a resolution.