I am typesetting a book of poetry using poemscol. I have run in to an issue where when poemscol is enabled in the preamble, the margin on the verso (left side) page moves over to the right side of that page.
NOTE: I've enable a frame to show where the textblock, header, footer and margins are.
\documentclass[draft,letter,10pt,twoside]{book}
\usepackage{showframe}
\usepackage{color}
\renewcommand\ShowFrameLinethickness{0.25pt}
\renewcommand*\ShowFrameColor{\color{red}}
\usepackage{lipsum}
%\usepackage{makeidx}
\usepackage{multicol}
\usepackage[osf,p]{libertinus}
\usepackage{geometry}
\geometry{tmargin=33pt,
textwidth=318.21pt,textheight=550pt,
marginparsep=7pt,marginparwidth=10pt,
headheight=15pt,
headsep=19pt,
footskip=15pt,
lmargin=132pt,twoside}
\usepackage{keyval,ifthen,mparhack,manyfoot}
\usepackage{fancyhdr}
\usepackage{poemscol}
\begin{document}
\leftheader{The Collected Poems of Robert Penn Warren}
\lipsum[1-12]
\end{document}
twosideand provides some history: Illogical twoside margins – barbara beeton Mar 14 '23 at 21:19