Bug 86377 'remove from build path' not working for class folders
Add as class folder to a project, a package folder from an other project. Select the class folder node and try to remove it from the build path using the context menu action Build Path>Remove from Build Path. The class folder is no removed and the selection in moved to the package in the other project.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/newsourcepage/BuildActionSelectionContext.java
if (!(element instanceof IAdaptable))
			return null;
		IResource resource= (IResource) ((IAdaptable) element).getAdapter(IResource.class);
		if (resource == null) {
			if (element instanceof IPackageFragmentRoot)
				return ((IPackageFragmentRoot) element).getJavaProject(); 
			if (element instanceof ClassPathContainer)
				return ((ClassPathContainer) element).getJavaProject();
			return null;
		}
		IJavaProject project= JavaCore.create(resource.getProject());
		return project;
	}
	public List getElements() {
		return fElements;
	}
	
	public IJavaProject getJavaProject() {
		return fJavaProject;
	}
	
	public IStructuredSelection getSelection() {
		return fSelection;
	}
	
	public int[] getTypes() {
		return fTypes;
	}
}