i've had some jumpers too. and yeah they can crawl away too. they can jump away anytime but i've heard that when you first put them in your tank you should keep it covered for a week or two till they get used to your tank.
Mine would eat at the top of my tank then get spooked and jump out (I think). I dont know how or why but I have found many a shrimp on the floor. You can try to block all ways out but my tank was covered and they got out.