Originally Posted by DiapDealer
Allowing to save an epub in an invalid state means Sigil would have to allow opening an epub in an invalid state. How would Sigil possibly know that the error is one that you intentionally saved it with and not one that it would normally fix? The only way I could see that working is by saving it as some other file-type; which is likely to cause confusion when people don't know that they need to open the new error-state-saved project file in order to pick up where they left off. I just don't see it happening.
It's better than being in a position where you've broken something, don't quickly see the error, can't save but have to end the editing session and be somewhere else! Auto-fix can lose data.