automake: ylwrap does not update parser.cc HELP!

Greetings,

I'm using automake 1.10, together with autoconf and libtool for a very
simple project which uses flex and bision.  The part that is causing
trouble is the parser: parser.yy.

parser.yy itself should be perfectly correct since it was taken out of
another project.  Bison correctly generated parser.h and parser.cc
(after renamed by ylwrap).  But apparently, ylwrap failed to update
parser.cc (i.e. do subsititution: s/y.tab.h/parser.h), so when I try
to compile, it will complain that y.tab.h cannot be found.  And now I
really have no idea what the problem could be.  Below is the
Makefile.am, please help me.  Thanks in advance.

lib_LTLIBRARIES = libpolyread.la
libpolyread_la_SOURCES = parser.yy lexer.ll polysys.hh