I'm using Gnome Terminal 3.6.2 on Ubuntu 14.04.
On my trackpad I'm frequently accidentally opening a new terminal (even though I've disabled tap-to-click), I think the prominent placement of 'Open Terminal' here is to blame. Can I remove that entry or re-order them? It would be great to have Copy come first and Paste second? I use those much more often that opening a tab or terminal (intentionally).
I can duplicate the behavior (in 13.10) with a mouse- right clicking and dragging diagonally right and down will open a new terminal, but only if done quickly. If I right click and pause then I have to left click the menu options as expected.
It's starting to become more clear: there is an intentional feature of the right click menu that allows a right click and hold followed by the release of the right click on the context menu item of choice, which coexists with the right click release followed by a selection of the menu item and second right or left click.
The problem for me is when I'm intending to right click release and then select a menu item and a perform a second click. If the cursor is already moving down and right, or if I begin to make that move before releasing the right click, I get the undesired new terminal. I may be unconsciously trying to optimize the operation by getting a running start, or it is just random mouse movement.