Talk Namespace with semantic links
From semantic-mediawiki.org
Fragment of a discussion from Help talk:$smwgNamespacesWithSemanticLinks
Well, if you look long enough for a meaningful reason you will find one. Reality has it that everything seems possible, so I will remove this sentence.
About your issue. I just tested on my test wiki by adding
$smwgNamespacesWithSemanticLinks[NS_TALK] = true;
after the enableSemantics
call and indeed properties may now be set and they also pop up in my query results. Also the help message at the top tells me that I may now add annotations to the talk pages in main talk. There must be something else in the water at your end since I cannot confirm your findings.