texmath-0.7: tests/writers/munder-03.tex
\underset{\frac{first\ under\ script}{second\ one}}{BASE} = \underset{\phantom{fail}}{\underset{\frac{first\ under\ script}{second\ one}}{BASE}}
\underset{\frac{first\ under\ script}{second\ one}}{BASE} = \underset{\phantom{fail}}{\underset{\frac{first\ under\ script}{second\ one}}{BASE}}