Extruding a bone error I started to extrude a bone for the other arm but this happened.  What's going on with it?

Blend file
You have Skeleton Sketching enabled.
Disable this option and use E button to extrude the bone or Ctrl+LMB while the torso bone is selected.



To make the bone symmetrical on the mirrored side, after you extrude the bone enable Forked in Extrude Operator panel while you have X-Axis Mirror enabled