When using the "Snow, real magic!" mod which allows snow to spawn on slabs, stairs, etc. And snow spawns on the Cfoam slab and if you try to remove the snow layer by any means (Such as replacing the snow layer with water, Shift right clicking, etc) a lava source block is spawned. Somtimes the block immediatly vanishes but sometimes it stays and you have to try and manually remove it using seperate buckets. The Cfoam stairs appear to be unaffected by this issue.

Here is a video of the issue in action: https://www.youtube.com/watch?v=zecTlRyegCo

@E100-cpu thats more a bug of Snow, Real magic not ic2classic.
Because it looks like it doesn't set the blockstates properly or delayed.