When the validation message appears that the Start Date should be before the End Date, picking a proper End Date does not automatically remove the validation message in the Gantt.
Workaround: call the validate method in the change event of the End DatePicker.
https://dojo.telerik.com/@martin.tabakov@progress.com/IQiRukIN/11
The validation message remains and the user must again focus and blur the Start Date picker for the message to disappear.
The validation should be removed automatically after picking a EndDate that is after the StartDate.