Candle Confusion

I've wanted to ask someone this for a long time. It may seem trivial--but that's what this blog is all about right?

So we have this candle at work in the bathroom (I work with two men and we share a bathroom). It is similar to the ones pictured above with the entire candle enclosed in glass. This is different from those glass candle holders in which you put a tea light--this candle comes with its own house like a turtle.

So everything is fine until the wick starts to burn down below the top of the surrounding wax. What the heck are you supposed to do to keep the melted wax from filling in around the wick and either putting the candle out or making it impossible to light? I've tried rolling the candle to get the wax to harden around the top--but that seems really stupid. Is this just a bad design or does the rest of the world have a secret that they are not sharing?