order of fileset matters?

I have two files in a fileset. Both files are present in the workarea.
When the order is "cpd_report.xml,simian_report.xml" an error is shown (see fileset1.png).
When the order is "simian_report.xml,cpd_report.xml" no error is shown (see fileset2.png).
Expected behaviour: The order of the files in the fileset should make no difference. Since both files are really present, no warning should be shown.