How to copy a master slide?
If Insert-->Duplicate slide is disabled, try this:
- Save your master slide you want to copy (main.odp)
- Save another copy of it to another file (new.odp)
- Open up the initial (main.odp) file so you have two impress windows open
- Open up the master view in each impress window
- Drag the master you want to make a copy of to the slide canvas in the center of the impress window (not the left slide pane)
- Now you will have a copy of the slide master you dragged over added to the bottom of the slide pane list