In digikam4 when I rotated the image both thumbnails and preview had the same orientation. In digikam5 it changed. So my thumbnails has original (just from camera) orientation even after I rotate them by hand. My camera has no orientation feature, so I'm forced to set the orientation by hand. Reproducible: Always
Update. When I rerun digikam the thumbnails were refreshed and displayed ok. So I have checked it once again with new images and digikam works nice now. So I guess it was stupid kubuntu 16.04 which can't mount at boot time cifs shares (at least wtih wifi) so sometimes I forget to mount by hand my /mnt/photos and when I mount them after digikam has started the problem above appears. P.