This right click behavior is not Gimp specific; it affects right click context menus (eg I saw it first in evolution). Seems to be related to themes. See Comments in (the duplicate) Bug 133071.
Specifically, Human and Outdoors are affected, but some other themes are not. I started playing around with this and found that if I chose the Human theme, then clicked Customize and chose the Mist icon set (and leaving everything else as Human), then right click context menus work fine again.
This right click behavior is not Gimp specific; it affects right click context menus (eg I saw it first in evolution). Seems to be related to themes. See Comments in (the duplicate) Bug 133071.
Specifically, Human and Outdoors are affected, but some other themes are not. I started playing around with this and found that if I chose the Human theme, then clicked Customize and chose the Mist icon set (and leaving everything else as Human), then right click context menus work fine again.