[O] Beamer export of a subtree seems wrong.

[Torsten Wagner]

Hi,
I recently started to prepare lecture notes in org mode. I used the example from Eric on worg as a template.
Everything works well. I used the first headline level to define groups of slides, the second level are slide titels and so on. A full export to PDF looks like expected. However, I thought I can do something like
* lecture 1...
* lecture 2...
* lecture 3...
and exporting only the subtree, I assumed should result in a PDF file for a single lecture. This does not work :( A subtree export with the pointer on a toplevel headline ommits all slide titles (all ** levels). I tried to be smart and added :noexport: to all but one lecture. However, that had no effect at all.
Any idea what might be wrong? Or did I misunderstood the usage of the grouping frames function.

All the best
Torsten