Version: (using KDE 4.0.82)
Installed from: Ubuntu Packages
Open KMenu, drag some app into the panel, take a look at the panel -- you don't see what will happen.
Why not give user a hand -- show the app in the panel already, just like it was dropped, but grayed out. This way user will be 100% sure what will happen.
*** Bug 169785 has been marked as a duplicate of this bug. ***
This has been implemented in trunk and will be part of KDE 4.2.