Hello,
I am using your tileView in my app.
I am using a tile that every item in it is itself a tileView of user controls.
I am having an exception when I switch the itemsource of the outer tile (which effects the inner ones as well as they are binded to it).
The big tile's itemsource is binded to a treeview's itemsource. 
Whenever there is a change in the treeview's collection (the tree has checkboxes the decide which tiles will be visible) I am updating the binding manually (getting the binding expression and updating).
In a converter I convert the collection (a ListCollectionView of the viewmodel class of the user controls, filtered into groups) that I got from the tree to a collection that contains only the groups that are checked in the checkboxes (the groups are the outer tileItems). 
In the converter I copy the collection and delete only the groups that are unchecked (not supposed to be visible).
The user controls within each group are binded to a boolean property that tells the visibility of the items (with a converter).
The problem is that sometimes when I update the binding, I get notification of a tilePositionChanged of the inner tileView (that contains the user controls). 
The position that I get is -1, and that value does not come from my viewmodel (I checked).
Than I get an exception thrown because the tileView tries to put an item's column property to -1.
This does not happen every time, only when checking or unchecking an item and than I refresh the binding of the bigger TileView(which the inner ones are binded to).

I hope you have enough data.
unfortunately i can't attach the code.

Thank you in advanced,
Tamir.