I've filed a bug report with Apple about this, but thought I'd post to this list to alert Applescripters.

If you have an open handler in an application and you drop on it a folder that has its "Stationery Pad" bit set, instead of processing it, the folder will be duplicated in place with " copy" appended, and the processing will then occur on the copy.

It's nonsensical to have a folder's stationery bit set, but it has happened to me several times in both Snow and Lion, for no explicable reason, apparently at random. I first thought there was some problem with my application, which originated in Leopard where this never happened. To debug, I first made a droplet that did nothing at all, and the behavior still occurred with the problem folders, so then I went looking for the cause.

The terminal commands GetFileInfo and SetFile will check for and fix this situation.