Updated #digiKam to 2.7.0 and now the exif orientation correction is not working anymore during import. Someone has the same problems? Did I miss to update some settings?
Metadata templates did not get assigned, too. I controlled the import settings and it seems as if they were changed. The metadata template was not selected anymore, but to rotate according EXIF was still set, but not working correctly. Changed the template and now everything is working fine again.