Yea it works SOMEtimes.. like 1 in a million times, or that's what it seems like... the depressing thing is, I don't even play on VH anymore... the aforementioned examples were on H (Baktria) and M (Saba) campaign difficulty. So, I play on M or sometimes H because I like to RP things and that includes resting times between wars... it includes, at least to some extent, reasonable behavious from an ally...

And it doesn't happen with every faction... In the above mentioned campaign with Baktria I also share a border with Pahlava and have been neutral with them in the beginning when they declared war on the AS, because I tried to stay on good terms with the AS, then the bastard Seleukids declared on me and I allied with Pahlava and have stayed allied with them ever since... It's strange but in the end, after taking India, I had to station forts on strategic passes and finally they'd keep the peace... I had to garrison these forts with substantial forces though... so yeah, now Pahlava has secured Persia so there's a "buffer" of Persians between two split-up parts of the AS so I've started taking over the eastern Sleukid kingdom (hehe) and we'll see what happens once I share that large border with Pahlava...