The only thing that remains is Joomla! somehow screwing up the #__extensions table. All Component Parameters are saved on that table, by Joomla!'s com_config component (take a look at the URL on your browser when editing the Component Parameters and you'll see where that com_config business comes from). By uninstalling and reinstalling the component you cause Joomla! to regenerate the component entry in #__extensions, apparently fixing any issues caused by the upgrade of the CMS.
That said, I have not observed this issue on any upgraded sites, except those upgraded from Joomla! 1.5 using jUpgrade.
Nicholas K. Dionysopoulos
Lead Developer and Director
π¬π·Greek: native π¬π§English: excellent π«π·French: basic β’ π My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!