markup in stanza number

[Alan Jones]

I had trouble using markups for stanza numbers inside of lyricmode.
However, assigning it to a variable seems to work around the problem.

bflat = \markup { "B" \flat ":" }

textA = { 
 \lyricmode {
    \override LyricText #'extra-offset = #'(0 . 9.1)
    \override StanzaNumber #'extra-offset = #'(0 . 9.1)
    \set stanza = "g:"
    i4 V i i " " i \markup { vii \super "o" } i V vi V2
    \set stanza = #bflat
    I4 V I I " " I IV I ii V I2
  }
}