I have 4 columns: "Not Started", "In Progress", "Completed", and "Notes". You will notice there is big gap at the end in the picture(the right side).
If I were to drag an item into that left over gap, the Task vanishes from the Board. I have verified that the Task does still exist. Also the Task's "State" remains in the last State is was in.
One solution you might suggest is to make the columns bigger, well I need to be able to show blank space in order to allow more columns to be created by the user. Showing the empty space helps the user.
I've also tried seeing if I cancel the "CanDrop" behaviour, but it does not trigger due to it thinking its still in the existing State. Here is a log of what happens when I move the Task from "Notes" to empty space.
Here is the DropBehaviourClass
And if you really want the WPF for reference, here it is as well.