To reproduce: please refer to the attached gif file: 1. Drop RadCollapsiblePanel from the toolbox on to the windows form. 2. Click on the form and press Ctrl+Z to undo the change 3. Observe that an error dialog popped up saying "Index and length must refer to a location within the string. Parameter name: length"
Hello,
In Telerik UI for WinForms R1 2019 (version 2019.1.117) we have decided to removed the option to interact design time with the ControlsContainer of RadCollapsiblePanel. This change has also handled the Design Time error scenario after Undo operation.
Regards,
Dimitar
Progress Telerik