I have the following situation:

• A listbox with data taken from a model
• All listheaders have comparators set for each direction (using setSortAscending/setSortDescending)
• The listbox should allow multiple selection

I was previously (i.e., ZK <= 5.0.8) using a ListModelList in my composer. I kept using it, calling setMultiple(true) on it, until I found out that the the sorting was broken. This is because the listbox doesn't see the original ListModelList , but a BindingListModelListModel, which doesn't implement Sortable, even when the model retrieved by getInnerModel() does. Thus, I was getting a message of the sort of "Sortable must be implemented by BindingListModelListModel" or so.

I suggest that either:
a) BindingListModelListModel supports Sortable, throwing a runtime exception when sort() or getSortDirection() are called on an inner model that doesn't implement Sortable.
b) Listbox/grid treat BindingListModelListModel apart, checking if the inner model supports Sortable.

I anyways bypassed the problem by offering a BindingListModelList directly from my composer.