Drowned spawners only work in biomes where drowned spawn

The bug

The drowned mob when used in a spawner appears to only spawn in its natural water biomes (e.g. river), in or out of water, but will not spawn in a non natural biome (e.g. desert) under any circumstance.
This contrasts other biome specific mob type such as the stray, which will spawn in any biome as long as they are used in a spawner.