Securing fence panels in concrete posts

[tabbycat]

I had a new lap fence put up last year using concrete slotted posts. The slots are a bit wider than the fence panels and I recently noticed that some of the panels were starting to warp slightly. I inserted treated 1/2 inch full length battens on one side of fence within each concrete slot. The fence fits snugly now and looks good. However someone has told me that when the fence panels/battens expand and contract in wet weather it might cause the posts to crack as the concrete around the slots is the weakest point.Is this right?
I would be grateful for some advice - if I have to remove the battens what would be the best alternative?