This does indeed roughly fix the issue (the sidebar does appear at the side), however, the page layout is still quite broken in less noticeable ways.
Such as all other WordPress pages having margins on .container and padding at the top of .page-area
View post on imgur.com
I’m now digging through the code and find https://github.com/publishpress/publishpress-series/blob/0725c798d3c629d92c7cfbdefd3a0f10cae326b1/seriestoc.php and https://github.com/publishpress/publishpress-series/blob/0725c798d3c629d92c7cfbdefd3a0f10cae326b1/addons/grouping/theme/primary/taxonomy-series_group.php where the comments at the top lead me to believe I should be copying these files and modifying them to work with my theme!
Perhaps that is the answer.
I don’t seem to be able to find that anywhere in the source :s
Where did you spot it?