That is just the way Click and DoublelClick events work:
Taken from MSDN:
A double-click is determined by the mouse settings of the user's operating system. The user can set the time between clicks of a mouse button that should be considered a double-click rather than two clicks. The Click event is raised every time a control is double-clicked. For example, if you have an event-handling methods for the Click and DoubleClick events of a Form, the Click and DoubleClick events are raised when the form is double-clicked and both methods are called. If a control is double-clicked and that control does not support the DoubleClick event, the Click event might be raised twice.
Please read all about it here:
Control.DoubleClick Event[
^]
Hope this helps, if you still have doubts please leave a comment to my answer.
Best Regards,
Manfred