In general, all Sort-, Filter- and GroupDescriptors of the grid are automatically cleared in two cases:
1. The ItemsSource of the grid is assigned null, i.e. the grid is un-bound so to say.
2. The ItemsSource of the grid is assigned a collection which has a generic type that is different from the generic type of the previous collection that was the ItemsSource, i.e. if the grid was bound to IEnumerable<Apple> and then suddently someone assigns as the ItemsSource and IEnumerable<Cat>, we have to clear all descriptors since they might no longer be valid.
Is one of those happening in your case? In case it is, you would have to cache/save the descriptor somewhere and restore it on the grid after the change has happened.
If you still have problems, could you please open a new support ticket and send us a dummy sample project that demonstrates the problems that you are having. We will take a look at it to see what exactly is going on and what can be done in order to change this behavior.
I hope this helps.
the Telerik team