As Peter points out in the comments, the issue in the linked post is about combining primes with carets (
^). The expression
q^'_0 is invalid LaTeX (it produces an error message even in LaTeX). Version 2.0 incorrectly processed this expression, but that was fixed in version 2.1, which was released back in October of 2012 (a few months after the post you cite was written). So the expressions have not parsed correctly for several years. The correct form should be
q^'_0. Note that
q^a_b is fine, but
q^'_0 is not because of the special way that TeX treats the prime.