A Google Webmaster Help thread reports that because .UA domains are currently not considered "root domains" by Google, the change of address tool doesn't work for them.
I am not sure if Google did not consider them root domains or didn't allow the change of address tool to work with those domains. But Google said, whatever the issue is, it will be fixed soon.
Jonathan Simon from Google replied to the thread confirming the issue:
I've alerted the team to this issue. .UA domains should soon be supported by the Change of Address tool.
Forum discussion at Google Webmaster Help.
