I was able to add an “Image” to a Master Page and now try to insert a “Positioned Box”.
The Button for “Insert Positioned Box” is enabled, but when I click it, nothing happens. A look into the source shows that nothing has been added.
Can these boxes not be directly inserted into a “Master Page”?
Update#1: I got it. I tried to double-click somewhere onto the page. Seems to me like a “focus”-problem; I could not see any cursor, when it failed. Even switching between “Design” and “Source” didn’t help.