To reproduce: follow the steps illustrated in the gif file. 1. Set Autosize = false. 2. Resize the control by increasing its height. 3. Change Multiline property to true. 4. Change Multiline property to false. 5. Autosize property is reset by doing 4. So set Autosize to false again. Workaround: Use only the Multiline property.
The AutoSize property should not be visible in the designer and whether the control can be resized should be controlled by the Multiline property.