I settled on adding an OPTION line to my org file to disable this behavior, since the documents I'm working on rarely need subscripts and I can use the LaTeX form when I do need to specify them.
#+OPTIONS: toc:nil H:3 num:nil ^:nil
The last part forces the export to recognize just the LaTeX form of specifying subscripts.
[[info:org#Export Settings][org#Export Settings]]
‘^’
Toggle TeX-like syntax for sub- and superscripts. If you write
‘^:{}’, ‘a_{b}’ is interpreted, but the simple ‘a_b’ is left as it
is (‘org-export-with-sub-superscripts’).
Mark