That would make many programs that use portrait quite odd to use. Phone, for one. Camera is odd when slide is open. Many-a-game. Browser portrait mode. OSK.

You could set your T&K lock to a very low value, and the phone will lock soon. Phone never locks with the keyboard open, touching the screen revives it.

It is true that one should be able to choose zero for lock timeout if for nothing else than completeness sake.