Thanks a lot, Paul. These differences don't seem to explain the problem, though. (Not to me anyway.)
I changed PlaceStyle, PlaceDepth and RouteStyle to the original values in the ShapeSheet, saved the file, reopenend it and the auto-layout seemed to work fine in the vdx-copy I had made. Unfortunately it threw "Wirtschaftliche Chancen" out of the visible diagram hierarchy and attached it's children to another shape. I thus deleted "Wirtschaftliche Chancen" and all its children (and their children) and added them again manually using the brainstorming commands to add subelements. The layout still is messed up in the same way. It seems that auto-layout
a) is trying to avoid the paper and
b) has special trouble laying out the children of "Wirtschaftliche Chancen".
The same procedure in the vsd-file yielded no results by just changing the page-properties.
Also, it seems the page-properties are changed by the auto-layout. I opend a brand new brainstorming file, added a mainsubject and after pushing the auto-layout button the properties were changed like in my problematic file.
One of the lines in the User Section (LastAppliedLayout) is due to the fact, that I had played with designs, I think. I can't see where the other line (OutlineWndPos) comes from.
Just out of curiosity. If you happen to have Visio 2010, does the auto-layout work differently for my file?