Steps to reproduce:
1. Create a WinForms application
2. Drag a RadRichTextBox control on the RadForm
3. Set the Anchor property of the RadRichTextBox to Top, Bottom, Left, Right
4. Run the application and type in a few lines until the scroll-bar appears
5. Click the scroll-down button on the scrollbar and you will notice, there will be more space added to the last line
6. Click the "Minimize-Window" Icon on the right-top corner of the RadForm

Result: System.ArgumentOutOfRangeException: Value of '239' is not valid for 'Value'. 'Value' must be between 'Minimum' and 'Maximum'.

NO WORKAROUND