groovy.lang.MissingMethodException if using class extending BigDecimal

We have a class extending java.math.BigDecimal, also a method having a BigDecimal argument
The method works fine if we call it with a BigDecimal object. If the method is called with an instance of the extending class, a MissingMethodException is thrown.

groovy.lang.MissingMethodException: No signature of method: ConsoleScript16.f() is applicable for argument types: (ExtendedBigDecimal) values: [1]
Possible solutions: f(java.math.BigDecimal), is(java.lang.Object), run(), run(), any(), any(groovy.lang.Closure)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.unwrap(ScriptBytecodeAdapter.java:54)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:78)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallCurrent(CallSiteArray.java:44)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:141)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:149)
at ConsoleScript16.run(ConsoleScript16:14)
at groovy.lang.GroovyShell.runScriptOrMainOrTestOrRunnable(GroovyShell.java:266)
at groovy.lang.GroovyShell.run(GroovyShell.java:517)
at groovy.lang.GroovyShell.run(GroovyShell.java:172)
at groovy.lang.GroovyShell$run.call(Unknown Source)
at groovy.ui.Console$_runScriptImpl_closure16.doCall(Console.groovy:904)
at sun.reflect.GeneratedMethodAccessor227.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:90)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:233)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:273)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:886)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:66)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:149)
at groovy.ui.Console$_runScriptImpl_closure16.doCall(Console.groovy)
at sun.reflect.GeneratedMethodAccessor226.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:90)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:233)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:273)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:886)
at groovy.lang.Closure.call(Closure.java:282)
at groovy.lang.Closure.call(Closure.java:277)
at groovy.lang.Closure.run(Closure.java:360)
at java.lang.Thread.run(Thread.java:619)