Thanks for your contribution - At this time we are only using github as the place to submit code fixes, the actual reporting of issues and testing fixes is still taking place on Joomlacode.

Please can you:

1) Open an item on the Joomlacode tracker in the appropriate area.

CMS Bug Reports: http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemBrowse&tracker_id=8103

CMS Feature Requests: http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemBrowse&tracker_id=8549

2) After submitting the item to the Joomlacode tracker, add a link to the Joomlacode tracker item here and make sure that you add a link to this GitHub issue or pull request on the joomlacode tracker item.

Adding link to the tracker http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=32055

@rawcat I don't think this parameter should be applied here.
The parameter is meant for the module chrome like in the html5 chrome. (see https://github.com/joomla/joomla-cms/blob/staging/templates/system/html/modules.php#L35).

Unfortunately that's the only module chrome in core which supports the tag. But other templates may support it. If you use such a template (or the html5 chrome) and apply the parameter also in the module itself, you would end up with a doubled article or section tag (or whatever you selected), which would be not what you want.

@bakual: Is this code actually used in Joomla!? I can't seem to find any reference to it.

The module_tag parameter? It's used if you change the "Module Tag" in the "Advanced" tab of the module settings to "html5"
Inspect the source after you changed it and see that it gets doubled.

I agree with the comments made here. This is not what that param is designed for. If you want to control that div then you should template override. Thankyou very much for your contribution but I'm going to close this one!