Problem with Selection.setFocus

Ok so … I have a problem.
I need an input text field to get focus when I enter one specific frame.
So I used this.


And it sets the focus just fine BUT here is the problem.
I can’t use backspace or del in that input text which is NOT GOOD.
I really need it to work with at least one of the keys.

Can anyone please help?
Any ideeas why it behaves like that?