Using Ubuntu 10.10 64bit r34328 (confirmed on 2.56a by MatthiasM as well).

With a 32bit float, painting some stuff on the image, adjust the display curves and notice the change. Then try paint on the image some more and the display of the curve is reset again until you adjust the curve points.

Also, if you enable repeated coordinates in the display subpanel and zoom out a few times, you eventually run out of tiles, as they start stacking along the left side of the screen.

I uploaded a small video of the problem to the public ftp at:

http://download.blender.org/ftp/incoming/Image%20editor%20bugs.ogv

Hopefully it doesn't get deleted too soon :)