I am puzzled by the lack of attention to the position of the 'other' thrust lever when it comes to actuating reverse thrust. If I have understood the logic correctly, reverse thrust can be actuated on engine 1 even if the thrust lever for engine 2 is not 'at or near idle'.
What situation might the programmers have had in mind where it is a valid combination to have engine 1 in reverse thrust and engine 2 in forward thrust?
Maybe not "in forward thrust", but if AB had designed the engines such that with a jammed single TL you were denied the ability to shut down the uncontrollable engine and then have REV available on the "good" engine, people would be crying foul about the designers denying the pilots control over their good engine. (The logic looks at TL position, not engine thrust, note)
Once you start generating scenarios with various primary flight controls (like TLs) jammed or faulty, its VERY difficult for a design to be bulletproof.
PS I don't believe that a jammed TL is currently part of the scenario for this incident, pending some definitive info (and a leaked CVR doesn't count as definitive in my book)