When I scale a layer down the resampling is done on the actual image data and the orginal image data is not kept im memory. As a result when I scale the layer back up again, image details are lost forever. This makes a working with Gimp very hard, because everytime I need to rescale something (up) I need to create that layer form the scratch and all previous steps I might have applied to that layer are lost.

Gimp should work the same way as other tools (like Inkscape or Photoshop) where the original image data is retained in memory, so it doesn't matter how often I scale (and I suppose other spatial transformations, like skew or rotate work destructive to) the quality of the layer stays as good as the orginal pixel data.