Does anyone know what causes these gas pockets around electrodes? Below is an example of what I'm talking about, and also one that doesn't have it for comparison. These are 12mm electrodes, Voltarc/Masonlite brand. It did eventually clear up, and the electrode looks fine. I'm not concerned that it will have an adverse effect on the tube, I'm more just curious about why it happens. 

We used to refer to that as "outside ignition" and it was usually caused by either an impurity that allowed for the alternate path, or the influence of the fill pressure and current level.  It usually will clear up and not really pose a problem unless it continues over a long term or if it is allowed to happen for too long during bombardment at high current.  (the potential problems are 1.)  anything that sputters off of the outside of the shell is lost/traps gas against the glass wall and 2.) the arc path around the ceramic collar can create localized heating on that portion of the glass envelop and cause it to fail.  Again, these are mostly only a danger during bombarding and if the tube stops doing it after a while of normal operation then it is not a big deal.)