ok i see the problem.. if you have the Memory Use set to default value (Average) they icon does not hide. Setting it to "Stay in Memory Longer" (as i keep mine) causes the hide functionality to work.
you can change that setting if you want to confirm my findings..
i've fixed the problem and posted a silent update, so if you redownload or run updater and force it to redownload, you should have the fix.
Going to try to correct one more bug (hidden system tray icon) before i publish the new version.