% LuaTeX, Version beta-0.70.2-2012062812 (TeX Live 2012)
% fontspec 2013/03/16 v2.3a
% Adobe Jenson Pro Opticals version 2.053
\documentclass[12pt,a5paper]{book}
\usepackage{fontspec,lipsum}
\setmainfont{Adobe Jenson Pro}
% \setmainfont[ItalicFeatures={Scale=MatchLowercase}]{Adobe Jenson Pro}
% \setmainfont[ItalicFeatures={Scale=1}]{Adobe Jenson Pro}
% \setmainfont[Scale=1]{Adobe Jenson Pro}
\begin{document}
What happens to Adobe Jenson Pro’s italics from the second page on? An
italicized paragraph continued from the first page is OK, but one
begun on the second page shrinks. Deleting temp-ajensonpro*.lua in
luatex-cache didn’t help.

\lipsum[1]

OK:

\itshape\lipsum[1]

\upshape\lipsum[2]

Not OK:

\itshape\lipsum[2]

\upshape\lipsum[2]

Not OK:

\itshape\lipsum[2]

\upshape\lipsum[2]
\end{document}