somthing related:
Player A grants acces to player B.
player B does not grant A acces however.
B can now build tracks connecting to A's rail. The connecting field of A's rail is becoming property of B now, causing A's rail to become inpassable.
note, i haven't re-compiled since you fixed the bridge issue from above.
A can not fix this broken track, without B first deleting it.
ps.: It gets even more complicated when catenary is involved, as it stays property of player A, which B can't delete.