I simply didn’t thought of that possibility. 
Another “better” workaround would be to export as RF64 WAV (see this post: > Won't Export Full Recording - #4 by Gale_Andrews ), but note that RF64 may not work in some applications (such as WMP).
That’s what I did now - and it worked as expected! 
Also the FLAC file I exported before created some warnings (“sample/frame number mismatch in adjacent frames”) when I used ffmpeg to transcode it to other formats.
Now using the RF64 file as input these warnings are gone, too.
Thank you very much!