...
After upgrading to v2.9.3 and enabling GAC, creating a transaction for Partner, the objects will not be filtered based on Partner’s Project. The objects will be filtered based on the project on which the user has the permission. You can achieve this by visiting Projects page in Connect.
...
GAC works on a fail-safe mechanism. Therefore, it is highly recommended not to disable this feature if you have created projects and entities using GAC permission model.
Disabling GAC with entities created under projects can invite unknown consequences in already running transactions.
...