For me, it's clear.
Phase 1. Placing Tile:
Volcano tiles are placed exactly like those in the base game, except you may not place a meeple on a Volcano tile.
You may, however, move the fairy after placing a Volcano tile.
So placing meeple on Volcano tile is forbidden only in phase of placig of this tile. In all other turns it's possible to move over Magic Portal, Flier, etc. on any tile (including Volcano) except tile, when Dragon is currently placed.