When posting comment to this answer my connection hicked up so pressing ENTER three times produced the following:
Shouldn't the progress image be loaded in the same placeholder?
It also produced three "Comment could not be submitted" messages (due to timeout probably) which is fine.
Decline reason can be found here.
Edit: as of May 21, 2013 it appears that when editing existing comment, there are no more loading indicators at all. They are still present when posting new comment though.