Oh yes, I have seen this and changed UpdateSourceTrigger to LostFocus. But I didn't give it much thought.
What troubles me though (and it is not Update Controls issue, but WPF binding in general) is I don't know how to keep DataTemplate alive while they are in use.
I have the following scenario:
TabControl with TabItems bound to a collection of ViewModels. Each tab item can be bound to a different type, but all inherit from some same base type.
When I switch tabs from one type to the other the previous tab fires property change (on ComboBox, DataGrid, ListView etc) with NULL values and ViewModel gets updated, UNLESS the two tabs are of the same type in this case DataTemplate is not discarded. I
tried not to recycle templates but it doesn't help.
So what happens is I have to check for NULLs in property setters. But if NULL is a valid selection then I have to write a lengthy workaround.
This behavior can be seen in famous Josh Smith's MVVM demo
http://msdn.microsoft.com/en-us/magazine/dd419663.aspx, and I tried all sorts of things to avoid it, but it looks like the only thing for now is to check for NULLs.
Update Controls just pass through this behavior onto view model.
I was wondering if you had come across this in WPF and may be have some thoughts on how to best deal with it.