Standard topic is not displayed when no context theme is available

Basically the context help works. But if I press F1 and there is no open dialog with a stored topic, the default topic does not appear.  The URL looks like this:

... /index.htm?rhcsh=1&rhmapno=131201

The same German help works normally. Here is correctly mapped to the default topic. The URL then looks like this:

... /index.htm?rhcsh=1#t=General%2FProgramwindow%2Fthemen_hauptfenster.htm

Why is the default theme not displayed when no context theme is available?

Thanks for your help.

Dieter