Wrong busy time with ical import (Notes Client)

I am importing calendar entries in ical format by dropping the file on the notes calendar. On a first glance, the entries seem to be correct, however, the created appointements are not honoured with the free/busy time information. A closer look tells that the $BusyName and $BusyPriority fields of the entry document are not set.

Any ideas how to solve that problem?

Thanks a lot.

Roland