Issue with hung client when adding comments.

Several users are seeing issues where the client gets hung when adding a comment or marking a comment as read. (spinner keeps spinning and the comment is not seen/refreshed). A screen refresh (F5) fixes the issues and does show the new comment, but this is annoying... This is seen in Firefox, and has been observed for several Collaborator versions (we are now on 13.8)

Is anyone else seeing this?  Any pointers?
I tried cleaning the cache but the issue comes back.

Marc