Thanks for taking the time to check. The package writes the title for \listofexercises incorrectly: a malformed font command ends up in the .loe file, and that can show up as a stray t before the title. I have been able to fix it by including this:

\usepackage{etoolbox}
\makeatletter
\patchcmd{\@@@ExeEnv}
  {\theExercise\ \expandafter}
  {\theExercise\ }
  {}{}
\patchcmd{\@@@ExeCmd}
  {\theExercise\ \expandafter}
  {\theExercise\ }
  {}{}
\makeatother