Setting the page-property ConsumeContainerWhitespace=true (in the properties dialog, F4) has helped. However it was anyhow tricky to build the report correct. At the begining it worked only if I added all extra content to the page-header and footer. But this was not acceptable. After a lot of trying, I succeed in making the report as desired. However I don’t really understand the logic behind.
I have in mind that I already have done such reports (growing in both directions, horizontally and vertically together) without any problems and I don’t know what is difference to this report here. For this report, it’s definitively reproducable that the ConsumeContainerWhitespace-property makes the difference. But why this never happens to me for similar reports I have done, I don’t know. Also I don’t know why I had first to circle around before the layout-engine accepted my design.