Cumulative Victory Points

[LDiCesare]

Can anyone explain me how/if these work?
I ran a few games in order to test them but didn't get consistent results.
In a first game, it seemed nations kept the points they had after 1 year, and so the number of VP augmented with time.
In another game, the score graph showed the same behaviour for Yomi but other nations who controlled VP provinces didn't appear on the VP graph.
Is there a bug in the graph or is the cumulative victory points victory condition broken?
It's a bit annoying not to be able to know since one can't start an MP game with this victory condition given the strong doubts I have about it.
So, does it work, and how?

[ceremony]

You are supposed to gain victory points for each victory point province you control, once a year, during the summer turn. The victory points should be cumulative, so you never lose them.

[PashaDawg]

I have not witnessed any problems with Cumulative VP's in the to MP games I am hosting. I hope there is not a bug, but no one has squawked yet.

[Archonsod]

When did you check the graph? From what I can figure, if you grab a VP location after summer, you won't get anything from it until the following summer (when all nations holding VP locations are credited). If Yomi was the only nation still holding VP provinces during Summer, it would be the only nation gaining VP's.
You can really irritate your opponents by raiding their VP provinces only in late spring, thus denying them the points for holding the province the entire year...

[Agrajag]

Ofcourse, they'll be expecting just that and bolstering their defences accordingly. And a well stocked fortification can also put a dent in your plans.