Version:            (using KDE 4.4.1)
OS:                Linux
Installed from:    Archlinux Packages

When I select an image and D&D it to a tag item in the tags folder view, I don't get the "Set as Thumbnail" action in the context menu. It sometimes works, but only for tags in the toplevel of the folder view.

For example assume the following tag hierarchy:
Persons -> Andi

I assign "Andi" to some image, go into tag folder view, select the "Andi" tag and D&D the image to this tag item in the folder view. 
Expected result: I get the "Set as thumbnail" action in the context menu.
Actual result: I only get the cancel action, or sometimes the context menu even doesn't appear at all.

D&D the image to the "Persons" tag sometimes seems to work. 
Note: Using the context menu for the image always works, only D&D seems to be affected.