....and another solution to add to it.
I use PDFCreator as a printer driver that outputs a PDF. Though I do not have the same problem as you I tried a variation of your solution using PDFCreator instead. The problem it appears to have solved is one of PDF conversion using Calibre losing the second of a double letter sequence and instead having a space in place of the second of the two letter sequence. Like 'all' being converted to 'al '.
Creating a new PDF first (using PDFCreator) then using Calibre to convert the new PDF to an ePUB seems to have solved the double letter problem.
Hooray! And thatks for the nudge.
