If no book is opened, gnucash still asks if the user wants to save changes when opening a book, although nothing is opened and no change was made.
This also occurs on High Sierra. If you choose a file to open, Gnucash will also ask you if you want to 'save changes' but doesn't specify 'changes to what?' A user might very well be confused that the first response of the app to opening a file is being asked to save. The dialog makes sense if you in fact have a file already open (though it could be worded more clearly) but certainly makes no sense if no file is open yet.
I reset the version from 2.7.x to 2.6.19 because I can already confirm it there, but I believe, it is there almost the whole 2.6 series.
Fixed for 3.3.