Labeling this as hard as fixing it will likely involve understanding a whole lot about text encoding.

I believe I'm also experiencing this issue. In my case, I'm completely missing "fl" from a word in the SVG. I suspect this "fl" is a ligature in LaTeX and thus, possibly, treated as a special character (like the original report). In the generated SVG file, I can see

    <g id="text_26">
     <!-- Directional flux (cycle s$^{{-1}}$) -->
     <defs>

which is correct.

Using matplotlib version 2.1.2 installed via conda, with the following settings:

    mpl.rc('text', usetex=True)
    mpl.rcParams['text.latex.preamble'] = [
        r'\usepackage{amsmath}',
        r'\usepackage{helvet}',
        r'\usepackage[EULERGREEK]{sansmath}',
        r'\sansmath',
        r'\renewcommand{\familydefault}{\sfdefault}',
        r'\usepackage[T1]{fontenc}',
        r'\usepackage{graphicx}'
    ]

This issue has been marked "inactive" because it has been 365 days since the last comment. If this issue is still present in recent Matplotlib releases, or the feature request is still wanted, please leave a comment and this label will be removed. If there are no updates in another 30 days, this issue will be automatically closed, but you are free to re-open or create a new issue if needed. We value issue reports, and this procedure is meant to help us resurface and prioritize issues that have not been addressed yet, not make them disappear. Thanks for your help!

This was fixed by #12928 + #14156.

Thanks for the update @QuLogic