[edit] mod issue or deprecated version issue, don't bother reading more [/edit]

I recently add a portal connection to ease access to a stronghold end portal, the nether-side portal being located at y = 120, the overworld-side portal at y = 25, and the horizontal coordinates match (considering the x8 factor).
Both frames are 3x3.

When I go through it in direction "nether to overworld", everything is ok, but when I come back, I catch fire from no detectable source.
This happens to a friend who joined me to defeat ender dragon too.
I first considered an invisible fire bug, but I only catch fire when coming back, and there is no lava nor fire in the vicinity of the portal.
I precise too, that it is the only portal behaving this way, every other one work fine (and I have many since I use nether as a hub (as everyone does I guess ^^).

This is not really annoying for me (I secured the area so no mob may bother me, and my stuff is greatly sufficient to withstand fire as no more than a display disturbance), but I could for other people, and I would like to understand.

Edit: I just "vanillazed" (1.9.2) my server to be sure, and the bug does not happen anymore, so this came either from a corrected bug, either from mods ... Sorry for posting for nothing.