Importing DNGs and exporting to TIFF now gives TIFF files that can be opened in Lightroom 5 without a problem. So old problem solved.
Tried to save as DNG and reopen in Lightroom for some finishing touches. No problem to open and after some colour and light corrections an even better result as HF allone.
I'm very happy with this new version. Result is worth the long wait.
Yours
Jürgen