\RemoveEmptyStaffContext deleting half a GrandStaff

[Steve Dunlop]

I'm typesetting some organ scores which will be open content upon
completion.  As with most organ scores, there is a GrandStaff, for the
hands, and a staff for the feet.  The desired engraving technique is to
remove the staff for the feet when it carries no notes.  It is important
to use a GrandStaff, not a PianoStaff, because cross staff beaming is
not in use and I want automatic adjustment of staff spacing.

Part of the GrandStaff being removed when only one of its staves carries
notes in a system.  This is undesired.

Any advice?

Steve