Me again, hope this isn't getting too tiresome, WW1G is really a superb game.
My 1915 French Grand Offensive was a spectaular success, helped in part by a major German attack the previous turn that went badly wrong for them. As can be seen in the attached screenshot, I have pinned a large Geman force in Sedan against the Belgian border.
According to section 9.3.1 of the Big Manual they should be isolated since Belgium is a full neutral, not granting Right-of-Passage to either side and having a diplomatic value of 2. This should make the country forbidden terrain for supply purposes unless I misread the rules. However, the German force is very much in supply and wrecked havoc on the BEF with a violent attack complete with bombardment in the Nov-Dec turn.
Any insights as to what is going on here? Thanks in advance.