So far, I've worked on 5 different documents, two that I converted from PDFs and three where I split an omnibus into its individual books. Since the only thing I do in calibre is say convert EPUB to MOBI, I'm pretty sure my problem is somewhere in Sigil.
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But then again... View Specific Format in calibre has just shown me that the EPUB has one cover, but the MOBI has two. But I'm not doing anything trick in the conversion; I'm not smart enough.
There has to be something in the document that tells calibre to process it differently. Could somebody tell me where I should start to look for it?
In case it's significant, the documents which came out with only one cover were the PDF files. To change the covers from the omnibus, I renamed the correct jpg to cover.jpg and edited cover.xhtml to reflect the change in size.
(sigh) Thanks.