Note stem centered if font.name changed in EasyHeads

[Viktor Mastoridis]

\version "2.20.0"
\relative c'' {
  \easyHeadsOn
  \override NoteHead.font-name = #"Ubuntu"
  a b c d}

Hello,

If I try to change the font.name in EasyHeads, the stem gets to the middle
of the note-head (see attached image).
And Lilypond says: "none of note heads `noteheads.s' or `noteheads.d' found"

Any clues?