I feel like you're on the verge of solving my problem; but so far no luck. I appreciate your assistance.
The 'details' and 'preview' panes, at the bottom and right sides of the window don't seem to be doing anything that you cannot do in View mode on the toolbar. I have the view setting as Details. As far as I can tell in W8 there is no "organize" on the
toolbar.
I am always in Details view when I attempt this. There are no thumbnails displayed. The problem isn't constant. It is intermittent. I'll try and fail and try again five minutes later and succeed. Because it seems to work later, I think you're on to
something regarding the thumbnails.
It's probably different on windows 8, but I haven't got a Windows 8 system to use to find out what the differences
are. I'm throwing up some screenshots though, to illustrate what I mean, in hopes it'll allow someone that does have Windows 8 to work out what they are.
In this first image, I show the three sources of thumbnails I've found so far:

Circled in Blue, the icons themselves, in this case set to medium. Circled in Red is the details pane, and in green the preview pane.
This one shows a details-icon view of what happens when you select a folder. Circled in red, a medium-size folder icon in the details pane, showing as its contents a thumbnail preview of one of the album covers inside it (there's two albums, each in their
own subfolder.) In green are the options to enable or disable both the preview and details panes. You'll note the preview pane is blank: It only works on files, not folders.
In order for the files to get locked, SOMETHING has to be loading the files to trigger the lock. In this case it's clearly something in windows explorer. All I've been able to find so far in 7 are these three thumbnail previews.
It seems to me what is happening is that the files are getting loaded to generate the thumbnails, setting the lock...and then aren't getting unlocked after the thumbnail's retrieved. In fact the lock only seems to get released if you leave the page that triggered
the lock and come back (that it isn't locked when you come back strongly suggest there's a cache involved, keeping it from getting loaded again). I'm not 100% sure of the conditions for unlocking it, as it seems a bit complicated, especially when subfolders
get involved. I've personally been able to reset it by closing the window and opening a new one, as well as hitting 'back' and re-entering the folder(but I tend to use 'back' to get out of subfolders too, so that took me one level higher up.)
7 at least only seems to load the file and set the lock if something actually does trigger a thumbnail generation. If all three options are off (or the ones which are enabled don't actually get to load a thumbnail), it never seems to trigger the lock. The
details pane is particularly insidious this way, because its preview is both hard to notice AND only gets triggered when you actually click on something. So if you're on a 'small icons' view and click a folder to delete it, the details pane loading the preview
is what triggers the lock, mere moments before you push delete.
It's entirely possible 8 does things differently; it might even be preemptively loading them or something. I have no clue; I personally have no desire to get or use 8 at all, and the amount of time I've ever spent using it wouldn't make it into the double
digits if measured in minutes. As such, I've got nothing other than speculation to go on.