Not sure what mod it is, but one of the mods in the pack plants saplings that would normally despawn, which isn't a big deal, except that if they drop on a rail block, they will replace the rail block.
Temporary workaround is putting non-plantable blocks under the rail, but still it consumes a rail block and makes Steve's carts tree farms difficult until you figure it out.
Not sure what mod it is, but one of the mods in the pack plants saplings that would normally despawn, which isn't a big deal, except that if they drop on a rail block, they will replace the rail block.
Temporary workaround is putting non-plantable blocks under the rail, but still it consumes a rail block and makes Steve's carts tree farms difficult until you figure it out.