I realized a similar problem - in IE11 and also in Chrome (and it affects both the acrylic and classic PA version):
When switching the views on the map (user photos, popular, recent, indoor), displayed photos which were visible in current the tab and shall be removed from a display on the tab being switched on are not hidden in most cases. But sometimes they are correctly hidden. Looks like the photos from an active tab are only painted over (in foreground) the other photos visible so far.
Anyway, F5 (refresh) works fine (workaround).
I am going to report this issue to virtual Panoramio admins, but our reported bugs were not acted upon (nor answered) very long time...