Indeed, once upon a time we used to be partners with Intersoft and we shipped our products together with theirs. We had every intention to make this partnership a strategic, long-term endeavor, yet some problems arose which led to the termination of the partnership and each company took its own way. Intersoft have nice products and we can only regret that things between us did not work out the way we had hoped for.
While the partnership lasted, we were contacted on several occasions by our customers about problems with r.a.d.editor - WebGrid integration. One of the problems was related to the editor, which we fixed, however the other problems were related to WebGrid. The most commonly voiced problem was that a field being edited with r.a.d.editor could lose its value (starts showing "undefined") if a user clicks a number of times outside of the bounds of the editor. We researched the issue extensively and it seemed to be related to the WebGrid. We contacted Intersoft on several occasions, however the problem was never solved - they thought that the problem is in our control despite the feedback they received.
We have not had any other problems with the rest of the telerik controls, integrated with WebGrid.
As to your question "is there any chance that Telerik will be open to support issues regarding interoperability with their former business partner?" - even though we are no longer partners with Intersoft we will work with our customers and Intersoft to address any challenges you guys face. We know that you don't care about the relationships of vendors and you expect results - we'll do our best to help you get those results.
With regards to "ditching" of telerik products, don't expect us to make a counter "recommendation" not to use Intersoft products. They have a great grid and it is more advanced than ours. We believe that customers could make an informed decision which products to use and not to use based on the requirements of their project and we would in no way want to influence you. We can only promise to work together with you to address any issues you face.
the telerik team