Just to be sure: You previously loaded the books onto the device, with no conversion, using a 0.7.x version of Calibre, and they worked? And you reloaded them, again with no conversion, using 0.8.0, and they were broken?
Downgrading is generally not recommended, nor is it officially supported. There are, sometimes, database changes that break compatability with previous versions.
If you want to downgrade, however, you can find all previous versions of Calibre on the projects' Sourceforge page
. Be sure to uninstall Calibre (this won't touch your settings or your library) before reinstalling an older version. You should also bear in mind that this can potentially break things. Another thing to keep in mind is that if you downgrade, you can't help any developers asking for additional info, so the bug, if it is one, may not be found.