Originally Posted by JSWolf
If it renders fine in ADE, then it is the fault of the other reading app(s) botching things.
Or you could say the same about the other readers:
If it renders fine in other readers, then it is the fault of ADE botching things.
The problem is neither is really true, or useful. As pointed out above, ADE has some bugs, but that's not really important here, because the bugs will not usually make something "render fine" that shouldn't. But ADE has also some extensions (page templates, conditional CSS) that are outside the spec, and other apps are not botching anything by not supporting those. ADE has also its font and default settings that may be different from those used in other apps, and if a book relies too heavily on them it will break when put in a different app.
What you could say is: if an ebook is valid ePub, then it's the fault of [whichever reader] not supporting it properly. But that's not really useful either. First, it's not enough that an ebook validates with epubcheck or flightcrow for it to be valid (validators have bugs and limitations too). And then, blaming a reading app doesn't help in making it work