As of now, the device does two different things: it renders/displays an ePub if you load it through ADE (Adobe), or Calibre, or by drag/dropping it onto the device or a memory card in Windows Explorer. If, however, you sync a Kobo-purchased book through the Kobo software, then rather than using an ePub file it uses its own "optimized" version. My understanding is that this will be addressed/corrected in an update in the near future. In the meantime, try this: log into your Kobo account in a web browser, and download the ePub versions of your purchased books into ADE. From there, send them to your reader. Alternatively, if you're comfortable/familiar with removing the ADE DRM, you have other options as well.
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