This is irrelevant to bidi and it is one of polyglossia's font issues where
it is unable to do proper font handling. To fix this you can have this
before \begin{document}:
\makeatletter
\renewcommand{\poemtitlefont}{\normalfont\large\bfseries...@rtl
\hebrewfont\fi\centering}
\makeatother
--
Best wishes,
Vafa Khalighi
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