Actually I thinks there’s a problem with the Gimp. I’m currently using the 2.9.6 nightly build version provided by the archlinuxcn repository, obviously running on Arch Linux.
Today the problem is even different. The filter is applied to the level correctly, if the level is as big as the image. If the level is smaller, then the filter is correctly applied, but then the level is translated to the up left corner (0,0).
I presume it’s due to some bug in the git code…