Issues with Multitenancy: Agent can see all customers and customer users

[kdev]

Hello!
We setup a new instance of OTOBO and installed the multitenancy plugin.
We then created a group, an agent and a customer. The Agent was assigned a different group than the customer. Yet, the Agent can search and find the customer and all customer users.
This doesn't align with the concept of multitenancy and is contradicting to the description in the documentation.

Any ideas why this is happening or which configuration options may be required to achieve true multitenancy?

Thanks!