@FXBindable not support object type

when i write following code:
@FXBindable
class Person{
	Date birth
}
and save with GGTS,
a exception stack would be generated as follow:
!ENTRY org.eclipse.jdt.core 4 4 2013-04-16 23:11:11.455
!MESSAGE Internal groovy compiler error.
!STACK 0
BUG! exception in phase 'canonicalization' in source unit
'E:\WorkSoftware\eclipse\workspace\groovy\src\test\Test.groovy' Attempt
to change an immutable Groovy class:
javafx.beans.property.ObjectProperty
	at
org.codehaus.groovy.ast.ImmutableClassNode.setGenericsTypes(ImmutableClassNode.java:88)
	at
groovyx.javafx.beans.FXBindableASTTransformation.createFXProperty(FXBindableASTTransformation.java:325)
	at
groovyx.javafx.beans.FXBindableASTTransformation.createPropertyGetterSetter(FXBindableASTTransformation.java:267)
	at
groovyx.javafx.beans.FXBindableASTTransformation.addJavaFXPropertyToClass(FXBindableASTTransformation.java:246)
	at
groovyx.javafx.beans.FXBindableASTTransformation.visit(FXBindableASTTransformation.java:192)
	at
org.codehaus.groovy.transform.ASTTransformationVisitor.visitClass(ASTTransformationVisitor.java:147)
	at
org.codehaus.groovy.transform.ASTTransformationVisitor$2.call(ASTTransformationVisitor.java:220)
	at
org.codehaus.groovy.control.CompilationUnit.applyToPrimaryClassNodes(CompilationUnit.java:1191)
	at
org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:623)
	at
org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:601)
	at
org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:578)
	at
org.codehaus.jdt.groovy.internal.compiler.ast.GroovyCompilationUnitDeclaration.processToPhase(GroovyCompilationUnitDeclaration.java:171)
	at
org.codehaus.jdt.groovy.internal.compiler.ast.GroovyCompilationUnitDeclaration.analyseCode(GroovyCompilationUnitDeclaration.java:2098)
	at
org.eclipse.jdt.internal.compiler.Compiler.process(Compiler.java:833)
	at
org.eclipse.jdt.internal.compiler.ProcessTaskManager.run(ProcessTaskManager.java:137)
	at java.lang.Thread.run(Unknown Source)