Miracle of all miracles, i had two slimes spawn in a swamp biome! This was on a new world generated with v1.7, and occurred when running v1.7.1.
I cannot confirm if this would happen with a world generated pre-1.7.
I'm having the same issue. I will try to build a spawning platform in a swamp, but my home base is next to a swamp and its been weeks and not a single spawn of a slime above or below ground.
Miracle of all miracles, i had two slimes spawn in a swamp biome! This was on a new world generated with v1.7, and occurred when running v1.7.1.
I cannot confirm if this would happen with a world generated pre-1.7.