Grimjaw, you seem to have the opposite experience from me.
What AI Ranking and Activation Bonus are you using?
Oriflamme, I have seen it happen even with the AI disabled, but I suspect those two things (AI difficulty setting and automated rail repair) are not interdependent, or hardly so. I have seen it happen up to AI setting easy, and either activation bonus setting. Given that I have usually been playing as the CSA, and considering Pocus' information regarding availability of resources as part of the equation, it makes sense that I'd see it more often when it comes to Union AI.