Aye, they also can screw with things like crops. Heat blocks, as far as I'm aware, are a vestigial part of Railcraft that can appear for any number of reasons, I think I've even had them appear just by my walking about. Its extremely vexing and I always just disable them when I roll a new instance, since they appear to have absolutely no purpose.
A similar story is the reason things like Arcane Lamps and the like can also disrupt crop growth and placement. Due to how Minecraft's light system, ahem, works, the only real variable over which one has control is the intensity of the light, not the spread. Thus, to make anything light a larger area than glowstone, you need what's colloquially called "lamp air," invisible, intangible blocks that output light. These blocks are usually at the same y-level as the lamp, which is why you have to put them one above your crops. The biggest exception to this that I've found appears to be ReactorCraft's tritium lamps, which create a huge sphere of lamp air when placed.