Comment 27 for bug 236778

Guys, the -proposed are proposed updates, if they work, they go as official updates in -updates.
If you choose to add proposed in your repos you can choose to update only the gnome desktop related files, log out and log in again, and you'll see that it's fixed. You don't have to update everything. On the other hand, you can be a bit patient and wait for the fix to be officially released in -updates, then try it out.
There's no cpu spike on my dual core processor after the update in -proposed (compare it with the GIMP loading on the attached screenshot)