I have one of the wireless one, and used the GE transmitter with the jumper set to behave as a contact switch.
I'm using some code I wrote in node.js to monitor the elk state, and then talking to my Vantage system to turn on the deck lights. I have an elk rule which speaks when the sensor has been violated and resets.
It's on a lower deck, and when I've walk tested it it seems to work fine. I haven't persuaded the cat to do a walk test ahead of me tho, so I haven't experimented with the sequence which is causing your problems. I'll try it with a basketball ( our racoons are basketball sized I think ) this weekend and see what I get. I'll have to start in the dead zone on the centerline of the unit and travel to an edge.
What I'm not following from your description is why the sensor, once back in the Ready state due to both sensors being tripped, isn't then reporting the _next_ motion.
Our neighbor's rugby-ball-sized cat does trigger the 'regular' PIRs out there. I think he does this to bully the raccoons.