On ns_veil, a gorge was bilebombing from the top of the vents in Double - the vent was welded, but the gorge's presence prevented the vent from shutting. I suspect this is not limited to a single map.

I'm fairly certain mappers can work around this themselves by how they setup their welables (ns_shiva and airlock, for instance). So this is really an issue with Veil, not NS itself.