Last modified: 2013-10-08 23:16:35 UTC
It is currently possible to access the source of an item in wikitext edit mode on the test system. Didn't try if it is actually also possible to save an edit. See for example https://test.wikidata.org/wiki/Q4976634
After some investigation the cause of this was that the item was imported from wikidata.org. Imports like this are currently completely broken and I am not sure it's worth the effort to fix it at the moment.
I wonder if this is because $wgContentHandlerUseDB is set to false on testwikidatawiki. (https://noc.wikimedia.org/conf/InitialiseSettings.php.txt) If set to false, ContentHandler would use the namespace, so it tries to represent it as an item, which it kind of does. But if it were set to true, it should just be rendered as text...
*** This bug has been marked as a duplicate of bug 51412 ***