This is what I did to fix the issue:
After the Nefarian fight, Hearthstone then immediately teleport back to the dungeon via the minimap icon. It seems that some players (suspected classes that have pets or guardians) get placed into combat during the Cho’gall fight and never exit combat—causing the Ragnaros teleporting/warping bug.
During the bugged Raganaros, after doing the Hearthstone/teleport trick, he no longer warped me continuously, but some members were still getting warped. Might be worth testing.