Depending on where you stand compared to rails, the game blocks you from deconstructiong rails with the same errormessage you get, when trying to deconstruct rails below trains/wagons.

Hmm, I see what you mean, the way the mod works is by placing small invisible cargo wagons in blocks it wants to block, so that's why that happens.
It doesn't seem to be a huge issue with bots since you just move away and they pick it up, but when it comes to mining by hand I can't really do anything.
You can get by with mining the signal and then the rail, but in the meantime I'll keep this in mind, so if I think of something better I'll try it out.