Question about halo effect

A few days ago, there was a lot of traffic in my neighbour's garden so I decided to take out the Bigma. I've not been very successful, hadn't the time to set up the tripod. However, in a few shots I came across this halo effect at high contrast edges. I've put a 100% crop below (no pp, conversion through LR3 with standard settings). Is this normal & to be expected? Could it be an artifact introduced by the UV filter? I've tried fiddling with the CA sliders in LR, but to no avail alas. I'm really sorry for exposing my ignorance so, but very grateful for any replies.