Animations view makes corrupt animations

I have a really strange problem with the animation view. I tried to animate an arm to move a little bit up so made a key frame went 20 keys forward, took the Y-Axis of the object and rotated it up and made again a key frame.

When I played the animation, the arm made some really strange movements, rotation wild around. I don't know what I've done false because I just changed the coordinates of the y-axis.

I've also made a picture so it's easier to understand what I mean:

I'm not sure if there is a real problem here - it might be how it looks when euler angles are interpolated in linear way. I can see that rotation values change on all axis, not just one, so maybe it has something to do with how your joint is oriented in bind pose.

When I made a simple rotation animation on one axis I had the same problem, all the axis rotating.
I think this has to do with wrong euler axis is being calculated first, its called gimble lock.
I just deleted the key-frames from the other axis.