Hi Hussein,
I am not able to reproduce the issue in v5.1.0.0 & v 5.1.0.37. Please refer to the attached screen shot and sample.
http://websamples.syncfusion.com/samples//Tools.Windows/F63376/main.htmPlease try to set the DockingManager's SetDockLabel method in DockingManager's NewDockStateEndLoad event. Please refer to the following code snippet.
[ C# ]
this.dockingManager.SetDockLabel(this.listBox1, " Products List");
Please let me know if you have any queries.
Regards,
Rajesh C