Logic Pro 9 Critical step input and paste problem in piano roll


I am close to my wits end with this problem that I cannot believe others have not encountered. So here's hoping for some help...)

I compose a lot of my music using the piano roll, sometimes copying and pasting notes, other times using step input. However I can be busy working on a selected (single) region in this way - suddenly the step input stops working, and I cannot copy or paste any notes.

The only way to continue working is to close the editor, deselect the region I'm working on, reselect it again and open up the piano roll editor again. Then it works - but can repeat the behaviour at any time, and in any case can be awful for work flow.

It is as if the program thinks I have deselected the region (which of course I haven't)

I don't recall having had this issue with Logic 7 - it's always been there on L9 but I am now so fed up, it is breaking the program for me.

Any help really appreciated.
Thank you.