z after bar ignored in line number computation for big initials

[eroux]

Using the tex file:

\documentclass[12pt]{article}
\usepackage{fontspec}
\usepackage{geometry}
\geometry{a4paper}
\usepackage{gregoriotex}
\usepackage{libertine}
\begin{document}

\gresetinitiallines{2}

\gregorioscore[a]{Big-inital-small}

\end{document}

and the gabc file:

name:Surrexit Dominus vere;
%%
(c4) Sur(d)ré(f_0fg)xit(f) Dó(g)mi(fe)nus(f) ve(g_h)re,(ixh_i!/ggof.) (;z) al(f!gw!h>)le(ghf_51fv_ED)lú(f!gwhgh>)ia.(gf..) (::z)

one gets the error:

! Package GregorioTeX Error: Score ended before finding the end
(GregorioTeX)                of the second line of a 2-line initial. Make sure
(GregorioTeX)                you have at least two manual line breaks in 
(GregorioTeX)                your gabc.

which shouldn't happen. (this is a real-life case, although it looks like an edge case)