latexmk with "nothing to do" overwrites `TeX-output-extension` to dvi

[hexaeder]

Hey! Thanks for providing this package, the only true way to compile latex documents :)

Recently I've discovered a weird problem. I am not entirely sure whether this has anything todo with auctex-latexmk.

I have a .latexmk file with luatex and pdf mode specification. If I compile the project everything works fine and TeX-output-extension is set to pdf. However if I invoke latexmk via TeX-command-run-all without any changes to the document, i.e. latexmk reports "there is nothing to do" the variable TeX-output-extension is set back to dvi and the next view command will fail. The tex-pdf-mode minormode is still active though.

Any idea whats happening there?