Originally Posted by bfollowell
Now that I know I can fix this by manually editing the opf, I have no problem, until I go back into Sigil and edit an epub for some reason. If I do that, Sigil removes my start page definition. I'm not really sure why but it does.
It does that because "start" isn't an accepted reference type for the Guide section of the OPF, according to ePub standards. It's not a Sigil problem.
See there for accepted values: http://idpf.org/epub/20/spec/OPF_2.0...htm#Section2.6
It's because of this situation that I started using the "preface" reference type in my ePubs to set the opening page. But it didn't work as planned for the Mobi conversion. I opened a thread when I faced this problem a while ago: https://www.mobileread.com/forums/sho...d.php?t=130969
Didn't get the answers I wanted, but I noticed that now my Calibre-converted mobi always open on the "Title page" (semantics set in Sigil) on Kindle. No idea why it doesn't work for you. Only thing I see different from my current files (compared to the one I'm talking about in the thread) is that I never used again "page-break-before: always;" in CSS after that. Maybe it is related?