I do think you are on to something, Barrie, I was watching that AI progressing in the Dispatch Window and it seemed to be doing just fine, but it did look like a long one. I tried to capture a Screenie of the D-W, but was too late.
I will try what you did and see what my version comes up with. I should have time today. If the AI is too long for the siding in it's path, would OR not diverge it to the main and the Player to the siding? Or if there is a problem with the AI Path, this may not be happening?
I am like you, I no longer use anything MSTS nor do I have the tools installed to be able to do any further investigation.
I do think the simplest solution would be if one of the really good people who write Activities for Open Rails would take this one and modify it to work with OR with the AI's and L-Consists intact.