When my nanostream is turned off for any period and re started it sometimes starts working backwards churning water and any crap it has sucked in over my poor unfortunates underneath it! Are these prone to doing this? I only have to put my hand infront of it to change the water flow but what happens after power failures sand would be blown up and over all my rock and corals. Is this something we just have to put up with!

Yeh this seems to be the case, i've got 4 in my tank and they do often start in reverse after being switched off!