Happens when the modules cooperator_worker_force and eater_member_card are installed.
If I create a worker using the Force Worker option, it's field eater will not be selected to "Worker/Eater" (unlike for a "usual" cooperator worker). Therefore the Member Card tab is not displayed. The user needs to manually select the option in the eater field.
This behavior is inconsistent, and an uninformed user will not know what to do to display the Member Card tab.
Suggestion : create a bridge module "cooperator_worker_force_eater".