OK, so I closed all instances of DO and tried to reproduce the issue.
Belive me, I really tried hard to get the unexpected behaviour back 
to no avail so far 
To be fair, it was not always reproduceable in the past, too.
Nevertheless, the labels of the folders are correct now, but still missing the content from time to time. Means, there are no files visible unless I presse F5 to refresh.
I already reported this here, no scripts involved, btw.