First up -- I am a web programmer, so that has definitely colored my opinion of this problem and how much CC is responsible for fixing it ASAP. My apologies in advance.
Occasionally when editing text box/block, your server will have an error when I click "save" and then you are stuck there with the "save" and "close" boxes nonfunctional. The only solution is to reset the entire page thereby losing all of the changes you have made in that mailing and without knowing which changes you made. This can cost hours of work and, frankly, is not acceptable. This does not happen often, but when it does (like a few minutes ago to me), it makes me not want to use your product anymore.
The solution is easy: Allow us to close the box and return to the document, or at least save the document, at any time. I recognize the issues that might cause for your side - but the critical item is not ever losing hours of work.
I have seen various work-around ideas posted telling us to not re-use previous blocks, not paste into the block, etc. Basically - do not use your product the way YOU programmed it to be used. If you do not want people to copy blocks then eliminate the ability to do so. If you do not want us pasting formatted text then do not allow us to do so. Again - the solutions are on Constant Contact to implement and not your customers.
Adding to this is the fact that I have had this happen even following these recommendations, so an overall way to override this aggravating bug needs to be implemented.