Every time I save my Krita painting as a *.psd I get anoter *.psd~ in the same folder. It is of sligtly smaller size than the *.psd itself. What is that?
Another question; Krita does not include an thumbnail in the *.psd file it seems. If I open the Krita psd painting in Photoshop and save it back, there is a thumbnail in my Windows 8.1 64bit.

Any idea?

A file that ends in ~ at the end is a backup of the previous version. I am fairly sure that we indeed do not save a thumbnail to psd files yet.

I know the tilde is a backup.

As for the thumbnail, it might just be that Krita doesn't know how to make PSD thumbnails.
The PSD exporter had to be made without help from Adobe, because Adobe wants people to sign contracts and pay money before helping them, and often those contracts make the GPL license impossible.

I thought so. Backup and Adobe protecting... a pity the *.psd is a standard format one can not do without... Thanks for answering.