It's definitively an Adobe Digital Editions bug. I
downloaded it, installed and opened your testcase, the text is completely messed up. Probably the other ereader companies uses the ADE SDK to workaround its bugs.
Try to report it to the
ADE forum. I suggest you to not mention Kobo, or you'll be ignored. Report it simply as an ADE bug and link the testcase. In the end, this _is_ an ADE bug.