I've experienced similar problems. However, it seems to be a more general problem with RC.  Whenever this happens, my CPU goes to 100% util.
I added my comments and observations to http://trac.roundcube.net/trac.cgi/ticket/1483956 but it seems that not much is happening there (and I cant do it).

Rgs, Ralf


-------- Original Message --------

Subject:	Re: bug with images in html mode
Date:	Thu, 25 Jan 2007 17:22:15 -0700
From:	Guy McArthur <guymac@gmail.com>
To:	users@lists.roundcube.net

So it seems this only happens with larger images, I tried an html email with an image at 140K, roundcube does not open the message (empty page source).