Can't get RemoveEmptyStaffContext to work

[Sven Axelsson]

It seems as if I can't get \RemoveEmptyStaffContext to work properly.
In the example below it doesn't do anything at all. The
RemoveEmptyVerticalGroup override does indeed remove the first
empty system, but the other two are still there. What am I doing wrong?

-- 
Sven Axelsson

\version "2.7.7"

common = { \time 6/8 }

musicA = \relative c'' {
    \common
    
    \partial 8 b8
    b4. b4. | b4. b4. | \break b4. b4. | b4. b4 \bar "||" \break
    \partial 8 b8
    b4. b4. | b4. b4. | \break b4. b4. | b4. b4 \bar "|."
}

musicB = \relative c'' {
    \common
    
    \partial 8 r8
    R1*6/8*3 r4. r4 \bar "||" \break
    \partial 8 r8
    R1*6/8*2 | \break b4. b4. | b4. b4 \bar "|."
}

<<
    \musicA
    \musicB
>>

\layout {
    \context { 
        \RemoveEmptyStaffContext
        \override RemoveEmptyVerticalGroup #'remove-first = ##t
    }
}