This is a problem since the very first beta.
Evasion active skill could and still can drop you from the borders of the floating platforms arenas.
Yesterday, I was playing a new gunslinger in Bloodtrail and when facing Edric (Final, Act I), I used the skill Evasion (teleport backwards) and fall from the arena border. The same occurs if you use Evasion or teleport skills close to the "energy" barrier that locks you inside the arenas, you can pass through and get locked outside, and forced to reload the game to respawn at Stormfall.