The following actions are not allowed in a board when Back Annotation
is active (i.e. the schematic is loaded, too):
adding or copying a part that contains Pads or Smds
deleting an airwire
defining connections with the Signal command
pasting from a board into a board, if the pasted objects contain
parts with Pads or Smds, or Signals with connections
If you try to do one of the above things, you will receive a message
telling you that this operation cannot be backannotated. In such a
case please do the necessary operations in the schematic (they will
then be forward annotated to the board). If you absolutely have to
do it in the board, you can close the schematic window and then do
anything you like inside the board. In that case, however, board and
schematic will not be consistent any more!