texmath-0.7: tests/writers/munderover-08.tex
\underset{under-2}{\overset{\phantom{fail}}{\underset{under-1}{\overset{\phantom{fail}}{BASE}}}} = \underset{under-2}{\underset{under-1}{BASE}}
\underset{under-2}{\overset{\phantom{fail}}{\underset{under-1}{\overset{\phantom{fail}}{BASE}}}} = \underset{under-2}{\underset{under-1}{BASE}}