Beats me. I did a copy and paste of your code and it seems fine. Rather elegant in fact. I did the same in a text editor and $\lambda_{max}=528nm$ seems fine.
Ubuntu 16.04; LyX 2.3.0. While we are not using Windows, I'd try the traditional Reboot (just because it's MS) and see if it helps. On 16 April 2018 at 04:06, Wolfgang Engelmann <engelm...@uni-tuebingen.de> wrote: > I select in lyx (2.3.0) in math > \lambda_{max}=528nm > > but get in the pdf output > > ̆max = 528nm > > why? (Debian stretch) > > Wolfgang > -- John Kane Kingston ON Canada