Game crash when going through a nether portal

1. I built a nether portal against a stone wall i built before
2. I switched the nether portal on.
3. I saw a zombie pigman going throug the portal, so I killed it.
4. When I approached the portal to get the experience, the game crashed a first time.
5. After a game relaunch, I moved the wall behind the nether portal from 1 brick away.
5. When i tried to walk thrroug the portal, the game crashed again