Most of the things here are not really bugs; rather, they describe situations when the Panel's behavior is not what you would expect.
You can not place an ordinary file or directory on the Panel. If you try to drag and drop a file from the File Manager window to the panel, it won't work. The only type of file that can be placed on the Panel are .desktop files, which describe launchers (and .kdelnk files, which describe lunchers in the format used by K Desktop Environment); any directory dropped on the panel will be interpreted as a menu — that is, all the files other than .desktop files will be ignored.
Editing menus other than the Main Menu is rather confusing. Menu Editor at the moment can not be used for this, and Properties item of the right-click menu is not too helpful either - for example, it doesn't allow one to change menu's icon (see la sezione Configuring a Menu for instructions for doing this). This will be improved in the next release.
The Global Menu (which you get by pressing the Menu key on the keyboard or by right-clicking on the panel itself), and the Main Menu (which you get by clicking on the foot icon) are configured separately. The reason is that you can have several Main Menu buttons on different panels.
The Screen Lock button does not lock the screen if "No Screensaver" is set in the Control Center.
The only way of changing Panel type (Edge, Aligned, etc.) is by choosing Properties->Type from the Panel menu: you can not change Panel type in Panel Properties dialog. Conversely, Properties->Background type allows you to change the background type (Pixmap/Color/Standard), but not to choose the actual color or image to use.