Holding the Ctrl key lets me remove objects from the current selection, which is great. However, it always bugs me that Rhino will not let me remove a curve or a surface from the selection during the Join command. That forces me to cancel the command, re-run it and start picking the desired objects again. With the hope that I will not accidentally pick some unwanted object again. Do you plan to fix this bug (or lack of a major functionality) anytime soon? 
Other commands, such like “Sweep 2 rails” etc, let me remove objects from the selection while holding the Ctrl key, but why Join is an exception and causes so much troubles with that?
P.S.: The “Undo” clickable option in the Command line only removes the last selected object, which is far from optimal. Also, it forces me to move the mouse cursor far from the objects.