"Assertion failed!"

[Daniel Rosen]

Hello all,

When I try to attach a balloon to a whole note, like this:

%%% Snippet begins
\version "2.19.21"
\new Voice \with { \consists "Balloon_engraver" }
{
  \balloonGrobText #'Stem #'(3 . 3) \markup { "I'm a Stem" }
  g1
}
%%% Snippet ends

I get the attached pop-up window.

Is this an issue on my end, or is it a bug?

DR

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