Please describe the problem:
This problem occurs when I resize the canvas size ("image -> canvas size"). If part of canvas in the image window is behind of another window, when the canvas image is resized the image window is shown wrong: remnants of the old canvas is shown yet.

The new canvas size is only repainted correctly when another window is shown in front of the remnant image, or the image window is minized/maximized.

Steps to reproduce:
1. Create a image (example: 640x400 px);
2. draw something in this image;
3. go to menu "image -> canvas size";
4. adjust the new canvas size (example: 200x400 px).


Actual results:
The new canvas size is shown wrongly (the image window is repainted incorrectly).

Expected results:
The new canvas size should be shown correcty.

Does this happen every time?
Yes.

Other information:
This problem occurs in the Windows version and Linux version (Ubuntu Hardy, for example).