Firstly, I would like to note that all UI controls are not thread safe controls in the whole Windows Forms platform (not just Telerik controls, but all controls out there). Here is an article on MSDN, describing how to make thread-safe Winforms UI application. This means that any control from the Telerik UI for WinForms suite is not thread safe as well and cannot be used outside the main UI thread. You should use an Invoke to update the controls in cross threading scenario.
I have prepared a sample project following the provided code and I was unable to reproduce the auto-scroll behavior if the MasterTemplate.SelectLastAddedRow property is set to false. However, the scroll bar is updated after adding of each new row which is normal behavior.
If it is not the exact scenario, feel free to modify the provided project on a way to reproduce the experienced issue and get back to me with it so I can investigate the precise case. Thank you in advance.
I hope this information helps. Should you have further questions, I would be glad to help.
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