I was in a battle with raffy1995 just now and my volcarona died to magma storm. I switched in slowbro, intending to switch him back out immediately to regen enough health to survive a hit and kill after sacrificing another poke, and when i tried to switch, he was trapped. It seems that if magma storm kills a poke on the same turn it traps it, the following poke to switch in is trapped. My slowbro was not hit with magma storm, and should have been able to switch out, since it was a clean switch Please investigate this bug, and potentially ban the move until this bug can be resolved.

I came across the same bug as well during battle against npc trainer. I defeated the npc's Pokemon with Magma Storm, then that npc's next Pokemon gets trapped inside Magma Storm, which I only found out because I didn't manage to KO that next Pokemon.

 

And FYI, this can last until Magma Storm's trapping ends, even if that next Pokemon is defeated and another Pokemon is sent out. I ends up trapping the two next Pokemon after I defeated one with Magma Storm.