Large Magma Slimes, which used to require a 3 x 2.5 x 3 area I believe, are now spawning on a 1 wide platform with blocks against one side and a gap on the other. See screenshot for an example of this.

The area for the spawning that I've witnessed this is essentially a 1 wide area based on them spawning on the center of the block as there is a wall to one side of the block in which they would be spawning on.

I believe only tiny magma cubes should be able to spawn on that area, and this was the case prior to the 1.8 snapshots.

Note: Searched and checked all issues containing the word "magma" prior to submiting, sorry if this is a duplicate as I could not find an existing report for this issue