Maybe this is a useful 'feature', when I open an ePUB, have Sigil REMEMBER that folder so next time I want to do a 'save as...' I directly am in that folder and not in some folder from a previous session, thus browse to the current folder to save a 'new version'. I have had several times I forgot about it and gave the file a new name and saved it and the file ended up in some other folder from a previous session I used Sigil.
<filed under category: useful, intuitive>
Cheers
So what's next? A special checker checking for forbidden words/links that will have an ePUB rejected from iBooks?