I believe that is also a property of an AC motor in which it can start running backwards depending on where the armature is relative to the magnets (hence the bushing and shaft bearings wear causing issue also) and where on the sine wave the power is when it cycles (something like that anyway). Most wave makers (and aquarium controllers like the RKE and APEX for example that I a familiar with have a zero-crossing detection so that the outlet isn't powered until the wave AC sine wave is at it's zero point so that for example a motor doesn't become locked when starting and stopping repeatedly). On the larger Koralia Magnum Pumps there is an electronic startup device to prevent this from happening (it may have changed now but they didn't used to be on the K 1-4 line). On the DC motor that is a different story all together. I use K8's with a controller now because I didn't want to take a chance on having a pump run backwards without knowing that it's not flowing properly.