Keith – escaping the underscores (that is, replacing _ with \_) seems to fix the issues. For example, the following:

$\texttt{CategoryToPreorder}(\mathrm{Obj}( \mathcal{C}\_1 ), \mathrm{Obj}(\mathcal{C}\_2), \mathrm{Obj}(\mathcal{C}\_\leq), \mathrm{Mor}(\mathcal{C}\_\leq) ) :=$

renders as:

$\texttt{CategoryToPreorder}(\mathrm{Obj}( \mathcal{C}\_1 ), \mathrm{Obj}(\mathcal{C}\_2), \mathrm{Obj}(\mathcal{C}\_\leq), \mathrm{Mor}(\mathcal{C}\_\leq) ) :=$