Alternative ending height

[Walter Hofmeister]

Hello,
    I am having problems getting both alternative ending brackets to line
up. Here is the problem:

harmonies = \chords {
    \override ChordName   #'font-family =#'roman
  %A section
    \partial 4
    r4
    \repeat volta 2 {
    d2. d d d d
    d2. g a d d
    d2. d d d a
    d2. 
    }
    \repeat volta 2 {
    a2. a d a d
    g2. d a d g
    d2 a4 d2. e:m e:m a
    a2. d g d g
    d2. d a
    }
    \alternative { { d2. }  { d2. } }

As you can see at the end, both alernative endings have the same chord name
overhead. Lily prints the first chord name under the first alternative
ending bracket but does not print the second one. This produces two
different heights for the brackets. How can I force Lily to print the second
chord name (D) and therefore have the two brackets line up?
TIA

Walter Hofmeister