camera going out of focus on video

[mesocyclone30]

I was using pro video mode for the first time shooting video of a train and the focus kept going blurry ever few seconds. I tap to focus and 3 secs later it goes out of focus again. ruined video. good thing i used my camcorder at the same time. anyone else have this problem? Do i need to let samsung know in case they need to do an software update?