Share 'lava won't move'

I received a 52 oz lamp for Christmas this year, and upon plugging it in the wax melted and congealed into one big glob that moved slowly up and down inside the globe. I returned it to Spencer's because i thought it was something wrong with the lamp...however after i got my new lamp i encountered the same problem. If any one could shed some light on why this is happening I would greatly appreciat…