EDIT

Andreas Kohlbecker wrote:

• when I set the subject to for example "Germany" I find no means to reset it to "Default" except of using the delete Button

deleting the preference equals setting it to default

• The function of the Delete button seems a bit strange: The Predicate is only set to Deleted. A general user would expect the whole thing to be vanished.
  
• Restore Default has no effect, what should happen when there are multiple properties?

What do you mean by "properties"? Subjects? Preferences?
In general the semantics of "restore default" for a given page is that ALL data available on the page is set to default (which is similar to all relevant preferences are deleted). But I have not checked if it is implemented such.

• I found out that after using the Status Selection Button a new property is being created. Does this happen when the first entry is not the default one?

• Showing the predicate string makes not much sense since this is always the same.

true, at least if ONLY 1 predicate type is edited on the page, which is not always the case, but at least in the table it should always be the case. Therefore a good label could replace the predicate table (anyway the current string should be replaced by a good label)