Issue with titlesec page styles and appendix in book class

Question

I'm using titlesec to set my page style in a book class. If I include an appendix, the header corresponding to the first chapter is "Appendix 1" instead of "Chapter 1".

\documentclass{book}

\usepackage[pagestyles]{titlesec}  
\newpagestyle{main}[\scshape]{%
  \sethead
  [\thepage][][\chaptertitlename\space\thechapter. \chaptertitle]
  {\ifthesection{\thesection\space\,\sectiontitle}
  {\chaptertitlename\space\thechapter. \chaptertitle}}{}{\thepage}
}
\pagestyle{main}
\usepackage{lipsum}

\begin{document}

\chapter{Foo}
\lipsum

\appendix
\chapter{Bar}
\lipsum

\end{document}

Answer 1

Just add \cleardoublepage before \appendix; probably a bad interaction between titlesec and the class.

\documentclass{book}

\usepackage[pagestyles]{titlesec}  
\newpagestyle{main}[\scshape]{%
  \sethead
  [\thepage][][\chaptertitlename\space\thechapter. \chaptertitle]
  {\ifthesection{\thesection\space\,\sectiontitle}
  {\chaptertitlename\space\thechapter. \chaptertitle}}{}{\thepage}
}
\pagestyle{main}
\usepackage{lipsum}

\begin{document}

\chapter{Foo}
\lipsum

\cleardoublepage
\appendix

\chapter{Bar}
\lipsum

\end{document}

Answer 2

titlesec/titleps doesn't set \chaptertitlename as a "marked" command. Perhaps it should. For the time being, just write:

\newtitlemark{\chaptertitlename}