Desktop Folder is really a great function - I have 4 folders on my desktop.
But there are two really annoying nuisance:

1. When I add a new item into a folder all icons are reordered even though they shoud stick to their places! What's wrong here?

2. When hovering the pointer over a folder a preview window of the contents appears hiding what's below. How to turn that feature off please?

The reordering of items is a known regression I believe. You may wish to check that a bug has been reported by the user who initially encountered it.

The ability to turn off previews does not yet exist I believe.

No1 is a known bug, fixed for 4.4.1: https://bugs.kde.org/show_bug.cgi?id=227157
Regards