I can confirm this behavior with SFML 1.6 and Windows XP SP3.
As long as the mousebuttom is held down and the resizing is in progress no event gets processed, but as soon as the button is released all the resizing events triggered during resizing come flooded in at once.
I would appreciate it if all the resizing events could be handled as they appear, but I read its a problem with Windows. (However with Qt, from which I was moving because it was much mightier and bigger in size than I wanted, this was possible.)
At least it would be nice if this whole redundant resizing events could be skipped easily.
I found someone asking a similiar question at
stackoverflow, and there someone else responded that he uses a thread for event polling to obtain real time behavior even while resizing and moving the window.