imagettftext function does not handle combining character properly

We installed php 4.2.2 with freetype 1.3.1 on our solaris 2.8 machine. We are using function imagettftext to convert UTF8 string to image file for Internet display. However, it seems that this function does not handle the combining characters properly. For instance, the sequence of unicode characters U+0061(a) and U+0308 (combining diacritics) is display as two characters: a and a square indicating not displayable. The correct result should be a character identical to U+00E4. We are wondering where the normalization is handled in this case, freetype library or inside imagettftext php function? Is it a bug in freetype library? If not, how can we fix it? Thanks, Ziying Sherwin P.S. I am not on the mailing list, please send your response to sherwin@nlm.nih.gov