There may be some chance event which explains this, but we were asked to report strange behaviour, and this is strange.
Some details:
I presume the Militarists had finally annexed the Minor in question, 'Minor 'A', perhaps in the turn which had just passed. I had expected this, and had worked quite hard to persuade Minor A's northern neighbour, Minor B, to accept my regime's guarantee. We were all contiguous and lined up North to South along the coast like so:
N. ^
---> Me (Player, Western Forests)
---> Minor B (Confeds)
---> Minor A (Farmers)
---> Major X (Militarists)
S. v
So it seemed to be going according to plan when I received a Vid-Com announcement that the Militarists had invaded my protectorate, we were now at war, and the former Minor B was now mine. I started marshalling the bloated Confederate militia I had just inherited, and moving them southward to meet the advertised invasion.
But there is nothing there.
When my units finally make it down there, the territory formerly occupied by Minor A, which should be swarming with Major X's now equally bloated militia as well their own regulars, all swarming northward in to my undefended territory, they find it empty, except for fauna and wildlings.
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I hope that description is good enough by itself for now. Since I'm more interested in playing than writing tonight, I'll just leave this report as is for now.
Also, the save-game from my last report, just below this, should have the event on it (maybe). I need to investigate more. I should be back later with an image, at least.
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It took me quite a while to realize there was actually a glaring problem here. But now that I think about it, it definitely seems odd. Has anyone else noticed anything similar, in v1.27 or earlier?