Version: (using KDE 4.0.82) Lock widgets, drag&drop any app to panel -- you won't see abort icon, so it seems it is possible to drop there.
SVN commit 820230 by aseigo: don't accept drops that we don't understand or when we are immutable CCBUG:163908 M +8 -0 containment.cpp M +6 -2 containment.h WebSVN link: http://websvn.kde.org/?view=rev&revision=820230
*** Bug has been marked as fixed ***.