Custom date range in Page Overlay (no replies)

I need a Page Overlay for a custom date range (like July 2 - July 13) but whenever I add it to the URL I get an error.

My URL:
http://mypiwik/index.php?module=Overlay&period=range&date=2013-07-02,2013-07-13&idSite=1

The error:
The date '2013-07-02%2C2013-07-02%2C2013-07-13' is not a correct date range. It should have the following format: 'lastN', 'previousN', 'YYYY-MM-DD,YYYY-MM-DD'.

FYI %2C is an URL encoded comma
It seems like it's parsing the date wrongly because it doesn't expect to see a range.

I tried some other period types not in the PageOverlay period dropdown - like '&period=week&date=2013-07-02' - and they seem to work.

Am I doing something wrong or is this a bug? Or is it even not supported (yet)?

Thanks
Thomas