I get into unexpected behavior when using nested classifiers.
* Create a classes diagram
* Add a package to the latter class diagram
* Add a class in the latter package
* Select the latter class in the model explorer.
* Create a child class (i.e. an UML nested classifier)
* Try to drag and drop the created nested class to the package
It will fail. It don't want to drop it in the package. When you are over the package, it does not draw the "not allowed here" cursor nor the "you can drop it here" cursor; instead, it displays the "normal" cursor and just do nothing at all if you drop it over the package.
Work around : create a class in the package using the palette. Note: do not create a nested class for now! Then, in the model explorer, drag the newly created class in the target container class (the one where you would like a nested class).
This work only using this work around. The class must not be initially created as a nested classifier.
Additionally, even if the above workaround is used to create a nested class B in an owner class A, there is no way to draw a containment relation from B to A. So there is no way for the diagram to express B is a nested class of A.
Any attempt to do so, expose the same trouble as above : the mouse cursor does not say OK nor not-OK, and when the mouse button is released, nothing is done at all.