Rigging has a weird reaction on spheres I'm currently working on this toy-robot shown in the first picture. At the top of its head I use two spheres to create some kind of an antenna, but as you can see in the second picture, it doesn't really react as desired, and both spheres draw two thin lines back to the spot they're placed by default before any changes of the armature. 

The lines come from the two "end-vertices" of the spheres.

As far as I can see, the spheres aren't connected to anything but the headbone, and every single object is connected the exact same way, so I don't understand why it only happens for the spheres.

Anyone who knows this problem and how to fix it?
For whatever reasons, hard to say without knowing how you weighted the model, those vertices have not been properly weighted.  Thankfully, it's easy enough to fix.  Select your object and switch to weight paint mode.  Select the appropriate bone.  'v' switch to vertex mode and select the vertex (probably a single vert, so just RMB.)  In properties/data/vertex groups, make sure your assign scale is set to 1.0 and hit the assign button.  (Selecting the bone earlier should select the appropriate vertex group automatically.)

There are plenty of other ways to do this, some of which would be easier, depending on how your model is laid out.