I disabled that the upstream changelog file is distributed in the debian package. The spread-sheet-widget provides two binary packages
libspread-sheet-widget and libspread-sheet-widget-dev and both usually have the same changelog.gz which is derived from ChangeLog in the source directory. I noticed the 1970 date when I build this via pbuilder but the date was correct when I build via „debuild“. So I guess this might be a bug in the dh_installchangelog module. For now I just removed the upstream changelog. Thank you for your help!
