I have noticed some behaviour that I have come accross before in svg applications relating to drag drop functionality, I am not sure this is something you have come across when testing

In short when dragging and dropping a container window in Firefox, it sometimes attaches itself to the cursor despite having released left mouse button you then need to click once more to release the window from the cursor (able to send demo avi on request).

I am testing on FF 3.5.7 and IE8 it seems to be an issue specific to FF, Jeff Schiller of codedread.com had the following to offer:

I suspect you are bumping up into this problem: http://old.nabble.com/SVG-dragging-problem-td26140730.html See the Mozilla bug they reference there: https://bugzilla.mozilla.org/show_bug.cgi?id=525591 I believe this is a change in Mozilla since I first published my script. In SVG-edit, we use -moz-user-select:none and evt.preventDefault() in the mousedown handler and it has gotten rid of this problem (see svg-editor.css and svgcanvas.js).

thank you