SelectAll() and mouse

[Krazitchek]

Hello, i have a textBox with textBox1.selectAll() on
MouseDown event to select all te content when the mouse
got the focus.

If i click (with left button) on the right of the text in
the textBox, it works, all the text in the textBox is
selected but if i click on the left of the text it does
not work.

Is it normal ? How to do to select all in all cases ?

Thanks.