Ah sry it should be the tropical set, tr_drop_firebird to be exact.
But I have to revoke my comment about the schrubs, the front of the tr_craft_ufo_fighter has the exact same problem and that is almost empty.
Also the other debris I meant, was actually on the edge of it's tile.
Notice that the blocked area is exactly one tile width?
And btw, how can you see the name of the map, or even of a special tile in game?