I can say that more clearly. The backspace feature for ending a block does not work in IDLE when attempting to end a block that had no indentation. Example:
>>> if a < 4:
          a = 0 # Assume this is end of the 'if' block; that you want to
                # return to column 1, in line below the 'i'. The use of
                # BACKSPACE in IDLE will fail to achieve the desired
                # result and will cause ERROR.

Another example:
>>> if a < 4:
          a = 0
          while b < 7:
                a = a + b  # Assume this is end of 'while' block; that
                           # you want next line to begin directly below
                           # the 'w'. Use of BACKSPACE in IDLE will
                           # work correctly. But if you ultimately want
                           # to end the initial 'if' block, BACKSPACE
                           # will again fail and result in ERROR.