[XeTeX] Kerning flaw with MinionPro & XeTex

[Alessandro Ceschini]

Hello everybody,

With the MinionPro font, if I try to typeset a localized
form(specifically, Serbian) of U+0431 "CYRILLIC SMALL LETTER BE"
preceded by U+0423 "CYRILLIC CAPITAL LETTER U", Xe(La)Tex doesn't kern
it the right way, because it provides me with a blatant case of
characters stuck together.  This doesn't happen if I process the
relevant combination through, for instance, PangoView. Neither does it
happen with other fonts like Constantia, which possess Serbian glyphs.
In fact, FontForge revealed me that MinionPro does have a specific pair
combination for this case. That implies that XeTex simply ignores it,
maybe because it involves an alternate glyph?
Here below is a .tex example:

\documentclass{article}
\usepackage{fontspec}
\setmainfont{Minion Pro}
\usepackage{Polyglossia}
\setmainlanguage{Serbian}
\usepackage{xunicode}
\usepackage{xltxtra}

\begin{document}
\fontsize{24}{24}\selectfont Уб
\end{document}

Thank you for helping me.