Bone loops, rotation goes haywire

I’m walking my dog. It’s back leg consist of bone1+bone2. I add rotation to bone2 so bone2 rotates separately from bone1. I then loop both bone1 and bone2 ten times.

I noticed that for each loop, bone2 begins to rotate clockwise, until by the tenth loop it is facing up to the sky. Bone1 however does not do this.

What the hell? What am I doing wrong? I’ve started from scratch many times, but it keeps happening.