TestNG - Parallel Methods Not Working

I have a testNG suite where I want all methods in all classes I've specified to be run:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE suite SYSTEM "http://ift.tt/19x2mI9">
<suite thread-count="20" name="SmokeTestSuite" parallel="methods">

  <test name="Test1" group-by-instances="true" junit="true">
    <classes>
      <class name="Class1"/>
      <class name="Class2"/> 
      <class name="Class3"/>
    </classes>
  </test>

</suite> 

However this doesn't run all the methods, its doing it one class at a time.

If i write my suite as the following it works - however having to duplicate code in this way isn't appealing/very time consuming.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE suite SYSTEM "http://ift.tt/19x2mI9">
<suite thread-count="20" name="SmokeTestSuite" parallel="tests">

  <test name="Test1" group-by-instances="true" junit="true">
    <classes>
      <class name="Class1"/>
        <methods>
           <include name="myAutoTest1"/>
        </methods>
    </classes>
  </test>

  <test name="Test2" group-by-instances="true" junit="true">
    <classes>
      <class name="Class1"/>
        <methods>
           <include name="myAutoTest2"/>
        </methods>
    </classes>
  </test>

  <test name="Test3" group-by-instances="true" junit="true">
    <classes>
      <class name="Class1"/>
        <methods>
           <include name="myAutoTest3"/>
        </methods>
    </classes>
  </test>

  <test name="Test4" group-by-instances="true" junit="true">
    <classes>
      <class name="Class2"/>
        <methods>
           <include name="myAutoTest4"/>
        </methods>
    </classes>
  </test>

  <test name="Test5" group-by-instances="true" junit="true">
    <classes>
      <class name="Class3"/>
        <methods>
           <include name="myAutoTest5"/>
        </methods>
    </classes>
  </test>

  <test name="Test6" group-by-instances="true" junit="true">
    <classes>
      <class name="Class3"/>
        <methods>
           <include name="myAutoTest6"/>
        </methods>
    </classes>
  </test>

</suite> 

Any ideas to why this could be occuring?

Thanks