Comparison method violates its general contract!

[Mike48]

I don't know what to make of this:

Sat Mar 09 17:20:09 MinimServer: exception while processing action request: java.lang.IllegalArgumentException: Comparison method violates its general contract!
java.lang.IllegalArgumentException: Comparison method violates its general contract!
at java.util.ComparableTimSort.mergeHi(Unknown Source)
at java.util.ComparableTimSort.mergeAt(Unknown Source)
at java.util.ComparableTimSort.mergeForceCollapse(Unknown Source)
at java.util.ComparableTimSort.sort(Unknown Source)
at java.util.ComparableTimSort.sort(Unknown Source)
at java.util.Arrays.sort(Unknown Source)
at java.util.Collections.sort(Unknown Source)
at com.minimserver.Server.sortAlbumList(Server.java:3461)
at com.minimserver.Server.access$10700(Server.java:84)
at com.minimserver.Server$AlbumListView.init(Server.java:9059)
at com.minimserver.Server$AlbumListView.<init>(Server.java:8995)
at com.minimserver.Server$AlbumListContainer.populate(Server.java:9150)
at com.minimserver.Server.populateContainer(Server.java:3440)
at com.minimserver.Server.access$12600(Server.java:84)
at com.minimserver.Server$ContentDirectoryProvider.doBrowse(Server.java:9906)
at com.minimserver.Server$ContentDirectoryProvider.browse(Server.java:9861)
at org.openhome.net.device.providers.DvProviderUpnpOrgContentDirectory1$DoBrowse.ac​tionInvoked(DvProviderUpnpOrgContentDirectory1.java:978)