Performance issue with trains and unreachable train stops

[SWeini]

I have a very large base (100x science multiplier) using vanilla trains using parameters (2.7k trains, 2.9k stations).
Vanilla trains go to a loading station (all named the same), then go to an unloading station based on its cargo content using the item parameter.

Everything runs fine (just enough for 60 UPS, Train Path finder ~1ms), but when I expand my base using bots, and I end up with loading stations that aren't reachable because the rails aren't built yet, the UPS drops considerably (Train Path finder ~5ms). I guess I can explain what's going on, a lot of idle trains suddenly want to go to that station (based on its train limit), but they can't find a path. And to know there is no path they have to search the whole rail network. And then they do this over and over again until the bots have managed to build the rails.

A search backwards from that train stop would show very quickly that there is no way to ever reach it, but as it seems, this does not happen. I'd really like if this was the case, because right now the only way for me to continue playing is to build new stations with a train limit of 0 and only go up as the rails have finished building.

Save file: https://drive.google.com/file/d/1kBoxm0 ... sp=sharing
To reproduce: delete some rail in front of any "Load [item=cargo-wagon][item=cargo-wagon]" train stop and increase its train limit