We already answered to your previous ticket.
For your convenience I will copy our answer here too:
the Expander's Header is a toggle button this is the reason for the
strange effect with the Enter key and the mouse click. If you still
prefer to place an edit box or a button inside the header than it is
better to edit the expander's template and to shrink the toggle button
not to occupy the whole header pole.
All the best,
the Telerik team