Strange issue with people picker

Hello,

A strange problem occurred and I am stuck on ideas, wondering if anyone has any insight to share.

We have a multi-tenanted SP2010 environment, and host web applications ranging from glorified document libraries all the way up to large integrated solutions.

Customer A wanted to package up their highly customized intranet and provide it to one of their sister companies (Customer B).

Spun up a new web application, created a new site collection etc.  Backed up customer A's site and restored into customer B's site.  Removed all Customer A users from all groups and lists on site, and was about to hand over to Customer A so they could go through and remove data etc etc.  Customer B site has it's own SiteSubscription which limits the people picker to the correct OU for them, and also set Customer B site's UserAccountDirectoryPath to the right OU for good measure.

Went to add permissions for Customer B to the site, and Launching People picker I can see the users in customer B's OU and not other OUs as expected.  Weird part is that I can still see users from Customer A as well .

Tried creating a new user in Customer A's OU, and people picker cannot see that new user as you would expect.  Took one of the customer A users out of the Customer A OU and into another completely random OU, can still see it in people picker.

So kind of baffled, site seems to be respecting the OU scoping, but it somehow has a reference to the "old" users.  Anyone have any idea how to remove them?

Thank you!