Ant - Pathelement with wildcard only works in Javac forked mode?

I encountered below issue when using Ant.

My ANT script snippets:

<path id="id.compile.classpath">
  <pathelement location="src/compile_lib1/*" />
  <pathelement location="src/compile_lib2/*" /></path>
<javac srcdir="${module.root}/${src.root}" destdir="${swap.target.classes}"
  nowarn="${javac.nowarn}" debug="${javac.debug}" fork="${javac.fork}"
  classpathref="id.compile.classpath"
includeAntRuntime="${javac.includeAntRuntime}">
  <include name="**/*.java"/></javac>

When set fork=”true” in javac task, the wildcard pathelement works fine,
but when forked is set to false, Ant seems failed to interpret wildcard
correctly. (compilation failed, due to classpath error).

Any suggestions
Thanks.

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Best Regards
foolhunger