XeTeX ⇒ Problem Handling ZWJ in Ligatures

[dukerussian]

Greetings.

I am typesetting some Church Slavonic texts in XeTeX. I have created my own font called Hirmos Ponomar. In Hirmos Ponomar, I have added several historical ligatures that I would like to use. An example of such ligature is the Ligature AY, which consists of Cyrillic Small Letter A (U+0430) and Cyrillic Small Letter U (U+0443).

Now AU should always appear separate except when specifically required to be joined. The way that they are required to be joined is by placing the Zero Width Joiner (ZWJ), (U+200D), between them.

In FontForge, I have created a character called a.u.ligature. Under Glyph Info, Unicode Value is set to -1. On the Ligatures Tab, I have the ligature defined as:
"liga1 Standard Ligatures Lookup 1 subtable" - afii10065(a) afii301() afii10085(u)
afii10065 and afii10085 are FontForge's names for Cyrillic Small Letter A and Cyrillic Small Letter U, respectively. afii301 is FontForge's name for ZWJ. afii301 (that is, ZWJ) is implemented in the font as a blank character of width zero.

The TeX document has been specified as:

Code: Select all

\documentclass[12pt,a4paper]{article}
\usepackage{xltxtra}
\newfontfamily{\slv}{Hirmos Ponomar}
\begin{document}
\slv{а‍у}
\end{document}

(Where inside the \slv I have Cyrillic Small Letter A, ZWJ, and Cyrillic Small Letter U).

I run xelatex to obtain a PDF.

The expected result should be to see the AY ligature. Instead, I see Cyrillic Small Letter A, a box with an X inside, and Cyrillic Small Letter U.

Additionally, at compilation, I get the message:
** WARNING ** Invalid CMap mapping entry. (ignored)

I am using:
XeTeX 3.1415926-2.2-0.9995.2 (TeX Live 2009/Debian)
kpathsea version 5.0.0
Compiled with ICU version 3.8.1 [with modifications for XeTeX]
Compiled with zlib version 1.2.3.4; using 1.2.3.4
Compiled with FreeType2 version 2.4.4; using 2.4.4
Compiled with fontconfig version 2.8.0; using 2.8.0
Compiled with libpng version 1.2.44; using 1.2.44
Compiled with poppler version 0.16.4

on Ubuntu 11.04.

Question: is there something else I need to do in the TeX source to be able to use ligatures? Or, is this a bug?

Thanks.