Cathing fire when using the nether portal

My friend and I has this server for our self, but every time we use the nether portal, we are almost guaranteed to catch on fire for a few seconds.
We have tried to wall in in in blocks that can't catch fire, on both sides of the portal, remove fire and lava near it on both ends and even have water on on side so you stand in water while teleporting, but only to know that we still catches on fire when we come through on the nether side.