libplist utf-8 conversion bugginess

Environment:
Testing on osx snow leopard using libplist-1.10, also tested on libplist-0.8

Problem:

Certain 'apparently legal' utf-8 sequences are not properly converted by libplist. These sequences convert correctly using apple's plutil -convert xml1, but not using plistutil (or the c library directly -- tested via python and ruby bindings)

The resulting plist conversion does not work when parsing by other apple tools.

To reproduce:

See the attached files. sample.bin.plist (original binary src plist) and sample.xml.plist (converted using apple's plutil).

Here's a plist dump of the sample

{
    ProblematicValue = "\Ud83c\Udf1fCute utf-8 art\Ud83c\Udf1f";
}

Try converting sample.bin.plist to xml with plistutil and examining the output with apples plutil:

$ ./plistutil-1.10 -i sample.bin.plist -o sample.lpl.plist
$ plutil -p sample.bin.plist 
{
  "ProblematicValue" => "🌟Cute utf-8 art🌟"
}
$ plutil -p sample.xml.plist 
{
  "ProblematicValue" => "🌟Cute utf-8 art🌟"
}
binbag:plistutil monti$ plutil -p sample.lpl.plist 
sample.lpl.plist: Unable to convert string to correct encoding

$ diff sample.xml.plist sample.lpl.plist 
6c6
<    <string>🌟Cute utf-8 art🌟</string>
---
>    <string>??????Cute utf-8 art??????</string>

Note, you can't see it in this forum, but the string "Cute utf-8 art" is enclosed on either side by a utf-8 star icon. using the sequence: "\Ud83c\Udf1f"