SelectInput will not work when subclassed

[Mortimerp9]

import com.quantifind.sumac._
import com.quantifind.sumac.types.SelectInput

class BooleanOrAuto(val default: String = "auto") extends SelectInput[String](Some(default), Set("true", "false", "auto")) {
  override def toString = default
 }

class Arsg extends FieldArgs {
  var buck = new BooleanOrAuto() 
}

will throw an exception

scala> val a = new Arsg
a: Arsg = Arsg@30d0c98f


scala> a.parse(Array("--buck","true"))
com.quantifind.sumac.ArgException: Error parsing "true" into field "buck" (type = class BooleanOrAuto)
usage:
--buck  class BooleanOrAuto auto

    at com.quantifind.sumac.ArgumentParser$$anonfun$parse$2.apply(ArgumentParser.scala:30)
    at com.quantifind.sumac.ArgumentParser$$anonfun$parse$2.apply(ArgumentParser.scala:22)
    at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
    at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
    at scala.collection.mutable.HashMap$$anonfun$foreach$1.apply(HashMap.scala:98)
    at scala.collection.mutable.HashMap$$anonfun$foreach$1.apply(HashMap.scala:98)
    at scala.collection.mutable.HashTable$class.foreachEntry(HashTable.scala:226)
    at scala.collection.mutable.HashMap.foreachEntry(HashMap.scala:39)
    at scala.collection.mutable.HashMap.foreach(HashMap.scala:98)
    at scala.collection.TraversableLike$class.map(TraversableLike.scala:244)
    at scala.collection.AbstractTraversable.map(Traversable.scala:105)
    at com.quantifind.sumac.ArgumentParser.parse(ArgumentParser.scala:22)
    at com.quantifind.sumac.Args$class.parse(Args.scala:39)
    at Arsg.parse(<console>:12)
    at com.quantifind.sumac.Args$class.parse(Args.scala:34)
    at Arsg.parse(<console>:12)
    at .<init>(<console>:15)
    at .<clinit>(<console>)
    at .<init>(<console>:7)
    at .<clinit>(<console>)
    at $print(<console>)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:734)
    at scala.tools.nsc.interpreter.IMain$Request.loadAndRun(IMain.scala:983)
    at scala.tools.nsc.interpreter.IMain.loadAndRunReq$1(IMain.scala:573)
    at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:604)
    at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:568)
    at scala.tools.nsc.interpreter.ILoop.reallyInterpret$1(ILoop.scala:756)
    at scala.tools.nsc.interpreter.ILoop.interpretStartingWith(ILoop.scala:801)
    at scala.tools.nsc.interpreter.ILoop.command(ILoop.scala:713)
    at scala.tools.nsc.interpreter.ILoop.processLine$1(ILoop.scala:577)
    at scala.tools.nsc.interpreter.ILoop.innerLoop$1(ILoop.scala:584)
    at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:587)
    at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply$mcZ$sp(ILoop.scala:878)
    at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:833)
    at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:833)
    at scala.tools.nsc.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:135)
    at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:833)
    at scala.tools.nsc.interpreter.ILoop.main(ILoop.scala:900)
    at xsbt.ConsoleInterface.run(ConsoleInterface.scala:69)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at sbt.compiler.AnalyzingCompiler.call(AnalyzingCompiler.scala:102)
    at sbt.compiler.AnalyzingCompiler.console(AnalyzingCompiler.scala:77)
    at sbt.Console.sbt$Console$$console0$1(Console.scala:23)
    at sbt.Console$$anonfun$apply$2$$anonfun$apply$1.apply$mcV$sp(Console.scala:24)
    at sbt.TrapExit$.sbt$TrapExit$$executeMain$1(TrapExit.scala:33)
    at sbt.TrapExit$$anon$1.run(TrapExit.scala:42)

but using SelectInput directly works:

class Arsg extends FieldArgs {
  var buck = new SelectInput[String](Some("auto"), Set("true", "false", "auto")) 
}