The prose renderer appears to be rendering some running text using \textrm (inside math?). That violates various Latex principles and defeats things like font consistency and aspects of layout, especially when done inside Sphinx.

That is, text and math ought to be separated: math can appear in text, but not the other way round.

Moreover, the prose backend should render everything that is wrapped into :math: using the Latex backend, to ensure notational consistency and single modification points for changing notation rendering. No other module should depend on internals like exposing the expand_exp function.