Follow the steps which are illustrated in the gif file:
1. Create new .NetFrameWork Telerik WinForm project
2. Set the MinSize of the RadForm1 to 300, 300
3. Set the MaxDize of the RadForm1 to 600, 600
4. Save the Form
5. Close the form
6. Build the project
7. Add new Telerik form, inherit from RadFrom1 via the Add New Item form and picking Inherited Form (Windows Forms). When prompted, pick RadForm1.
8. Resize the new form
9. Save and Close the form.
10. Open RadForm1
11. Reset the Max Size
12. Save and Close RadForm1
13. Rebuild the project
14. Open the inherited form
Workaround: instead of adding an Inherited Form, add a Telerik RadForm. Then, change it to inherit from RadForm1: