Describe the bug

To Reproduce
Use the following as the source of the LaTeX
F_n=\frac{5V_m}{\sqrt{g}}

            MathListBuilder mlb = new MathListBuilder(inputLaTeX);
           Trace.Write(mathList.StringValue);

Output is this:
F_{n}=\\atop{0,515V_{m}}{\\Sqrt{g⋅L_{WL}}}

which is invalid

Expected behavior
Source LaTex produces this

Round Trip produces this:

These images are from http://www.wiris.com/editor/demo/en/developers

Environment (please complete the following information):
using CSharpMath.Atoms;
using CSharpMath.Enumerations;
using CSharpMath.Interfaces;
.Net Core 2.2