texmath-0.6.7: tests/writers/munder-06.tex
\mathrm{-\ middle\ -}=\underset{\phantom{\mathrm{fail}}}{\underset{\phantom{\mathrm{fail}}}{\mathrm{-\ middle\ -}}}\mathrm{-\ middle\ -}=\underset{\phantom{\mathrm{fail}}}{\underset{\phantom{\mathrm{fail}}}{\mathrm{-\ middle\ -}}}