When a road with routing instructions gets changed, those instructions will take precedence over the actual connections of that road.
That means, if one changes the overtaking mode from Two way to One way, cars will enter that road in opposite direction.
When one removes a connection in between two roads but remains the roads itself (unconnected to each other) cars will simply drive over the pavement or gras in between those roads.
How to Reproduce?
1. Load any save with calculated routes
2a. use the "set overtaking mode" tool to change the overtaking mode of a road
3a. enjoy wrong-way drivers
2b. use the "remove roads" tool on two adjacent tiles of a connected road
3b. enjoy cars simply pasing the grass
Whenever the ribis of a road change, all routing instructions to removed directions need to get invalidated.
Thank you for the report. I believe that I have now managed to fix this. I should be grateful if you could re-test in the next nightly build.