Wishcraft provided me the link for the newest version of the module (http://cid-6580d2a11c091017.skydrive.live.com/self.aspx/XOOPS%20Modules/Multisite/Source/xoops2.3%7C_multisite%7C_1.22+Patch.zip), which he said, is not officially released, but it works for me better than the 1.17 version, since it comes with all the patches to the XOOPS core inside.
One bug I have already identified:
Parse error: syntax error, unexpected '}' in /.../htdocs/modules/multisite/class/domain.php on line 613
You just have to delete the very last parenthesis in domain.php.
After that everything is working fine, except for trying to set the system preferences for each domain:
http://www.example-domain1.xyz/modules/multisite/admin.php?fct=preferences&op=show&confcat_id=1&domain=http%3A%2F%2Fexample-domain1.xyz
results in the following:
Fatal error: Call to undefined method MultisiteDomainHandler::getDomainOptions() in /.../htdocs/modules/multisite/admin/preferences/main.php on line 438
I will try to resolve the bug ... since this is a great module