python-dateutil will be updated to version 2.x and there may be changes that affect this package. If calibre will work with the newer python-dateutil, you can safely close this bug. If calibre really does require python-dateutil 1.5, please use Requires: python-dateutil15 for Fedora versions of the package until it can be updated.
On reviewing the list discussion, calibre should be fine here per Zbyszek.