Last modified: 2013-05-15 10:30:18 UTC
When I double click a headline to select (and copy and paste) it, a trailing space is selected, too. I tested this with both Firefox and Internet Explorer. This doesn't happen in older versions of MediaWiki, so the space probably came in there when the position of edit section links was changed.
I think this was fixed earlier by https://gerrit.wikimedia.org/r/#/c/63287/ (not deployed to Wikipedia yet).