Environment: 
Windows 7 Pro 64.
Core i7 2600K @~4.2 Ghz 8 Gb Ram.
Gimp 2.8 (about box only says 2.8) the installer was downloaded today (may 11).

Issue:
When opening certain images (for instance todays featured wp image:
http://upload.wikimedia.org/wikipedia/commons/3/39/Koppelpoort_Amersfoort_Cropped.jpg)
The following behaviour appears:

All manipulations of the image are slow. As in rendering Gimp nearly useless.
In comparison with Gimp 2.6.4, which I run in portable mode on the same PC, the 
new version achieves far less than 1/10th of the speed when, for instance, 
I am using a drawing tool. My estimate is that it is likely less than 1% 
of the speed of what 2.6.4.

It almost seems that it is the actual presentation of the image that lags. 
As soon as I attempt to draw or manipulate something I get an enormous 
delay between what I do and the result I expect to see. Using a filter does 
not seem to be much slower than before, however the updated image is drawn
gradually one block at a time on screen at a very low pace.
Gimp also causes a huge CPU spike when it attempts to update the image even 
when doing simple things like flipping it upside down.

This does not happen on all images and the problem depends on whether I open
the image or if I, for instance, copy it from the clipboard so it is a rather 
odd behaviour. In the instances where I have made a clipboard copy it always
seems to work fine.

To reproduce:
Save the image file indicated above to disk. Open it and try to draw on it.
Compare this to opening the image in a browser and copying it to clipboard 
and then pasting it in Gimp. The latter should cause no slow behaviour.


Best regards