::
Ok, I understand the why. It’s link to the way \setlinenum works.
So the solution is to add, in the preamble, this command :
`
\newcommand{\restorestanzaline}{\line@num=\thestanzaline}
`
And to replace
`
\setlinenum{\thestanzaline}
`
by
`
\restorestanzaline
`
