Created attachment 213523 [details]
Graphical artifacts/slow responsiveness encountered when Spacebar+mousing around an image's edges

Let me know if this is related to bug #674051.

Steps to reproduce:

1 - Create any new image of a convenient size.
2 - Hold Spacebar to activate scrolling mode and begin moving the mouse in various directions, scrolling both on and off the edges of the image.
3 - GIMP starts showing graphical artifacts and GUI responsiveness becomes very sluggish.

I haven't actually experienced any crashes yet (GIMP seems to recover in a second with no problems), but the slow responsiveness is definitely an issue.

This behavior does NOT seem to occur when scrolling via mousewheel, or when scrolling fully within the image edges - only when scrolling around the image edges (which happens to me a lot because that's the only context where mousewheel scrolling alone won't work).