UBB.threads PHP Forum Software Community Forums UBB.classic UBB.classic 6 Support multiple content islands, moving problem

I am running ubb classic 6.5.0 on a unix box. it was installed by the ubb support team and has been working perfectly.

I have amended the setting to allow multiple forums to be on a content island.

I have 2 content islands, call them A and B

I use the CSS included file option for both CIs

A has latest posts from forums 1,2,3 displayed
B has latest posts from forums 4,5,6 displayed

If I move a topic from 6 to 3 then it should drop out of island B and be inserted in to island A

What actually happens is that it gets added to A but is still in B, but pointing to a "this topic doesn't exist page".

I have cleared the cache, rebuilt forums stats etc, EVEN DELETED THE CI AND REBUILT IT but it still shows the same. I suspect its a bug somewhere. Have trawled the source code but it is not obvious.

Any ideas, or better, fixes ?

Thanks