The same wierd thing happens to my USB Mass Storatge device regularly. But with a .exe extension to it. If i tell you in detail...
Suppose I am having a folder named "DIGIT" and have some files inside that folder. If I open that folder ther will the a sub folder in it with the same name("DIGIT") even though i never created it.when i double click it, I will get "MyDocuments" in new window. First i'm confused. Then i went to folder options and tweaked to show the file extensions. Then i happen to see that the name of the duplicate folder is "DIGIT.EXE". when i scan it with antivirus... boom.... it's a trojan virus.
If I double click it without knowing it... when i restart my computer... all the folders in my pc would have a that thing. Which is very annoying. Things go pretty wierd then.. one by one your hide folders can't be visible, you cannot enable task manager,etc.
Scan your files with a good updated antivirus. NAV 2009 should be a good option.