Bug: adding song more than once to set results in loopback

[Stichting Bon Artz]

<?xml version="1.0" encoding="UTF-8"?>
<set name="testset">
  <slide_groups>
  <slide_group name="Bitter Zeemanslied" type="song" presentation="" path="Duvels Akkoord/"/>
  <slide_group name="D'r wou nen boer ns vruug opstaon" type="song" presentation="" path="Duvels Akkoord/"/>
  <slide_group name="Fransman" type="song" presentation="" path="Duvels Akkoord/"/>
  <slide_group name="Bitter Zeemanslied" type="song" presentation="" path="Duvels Akkoord/"/>
  <slide_group name="Hee gaode mee" type="song" presentation="" path="Duvels Akkoord/"/>
</slide_groups></set>

The above set (created with desktop companion app) results in the Android app endless loop from song 4 to song 2.