You are right, it is called not from the UI thread, this is a bug. I have logged it in our backlog and I have created a public item in our Feedback portal
which you could follow in order to receive notifications about the bug status.
I have updated your Telerik Points as a token of our appreciation for reporting the bug.
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Feedback Portal
and vote to affect the priority of the items