XnView Software

I can't reproduce
Ok - but I can reproduce it:
start with selecting a large image in thumbs view - doubleclick -> fullscreen display (OK so far)
doubleclick on image - single image is shown (instead of thumbs only view like when using "enter"!)
doubleclick again - thumbs are shown again ...

Check freeing of system ressources after closing fullscreen images directly to the thumnails - when repeating that procedure there's a multitude of fake MDI-system-controls (min,max,close) loaded - obviously left-overs from previous full-screen display (just one image allowed mode).
?? Which OS do ...

1. problem : after importing images file-handles (one up to multiple!) are kept open on the SD-Card - thus causing safe removal to fail (unlocker.exe helps)
Suggestion: employ correct use of close(filehandle/dirhandle) and possibly check that those calls are performed even in case of internal ...

Regarding latest XnViewMediaDetector

please see: http://newsgroup.xnview.com/viewtopic.php?f=36&t=17870

Regarding latest Xnview :
Check freeing of system ressources after closing fullscreen images directly to the thumnails - when repeating that procedure there's a multitude of fake MDI-system ...