So, this appears to be a Joomla issue, not spawned or native to ECWID.  But, perhaps the happy marriage of Joomla and ECWID has birthed you a problem child

I'll actually be at a conference next week (Austin, Texas) with ECWID and can ask them in person.  For the now, have a look at a similar question/answer I found for you on the ECWID forums:

Source: http://www.ecwid.com/forums/showthread.php?p=55061

Hope this helps!  Cheers.