Saving epub to disk missing letters

When I save my epubs to disk, some of the authors and series names have missing letters, making them scrambled. Example:

"J. Steven York" comes out as "J. Sten York"

Many authors come out like this, as well as various series names.

My save to disk template is thus:
{author}/{series}/{title}/{series}{series_index:0>2s| – | – }{title} - {authors}

Am I doing something wrong here?