This is with Translate 2014-02-04.
I've created a testcase which you can see by visiting https://www.mediawiki.org/w/index.php?title=User:SamB/tvar_bug&oldid=907218&action=edit§ion=1 and clicking the "preview" button.
Notice how all of the Translate markup shows up in the Preview because the <translate> tag isn't in this section? That's kind of annoying.