After a good while bouncing between different ZC versions to try and figure out why only one of three equally-configured attributes could be added to the cart, I found that the permitted attribute was the only one with a POSM model number assigned, despite the module being disabled. Deletion of the POSM entry restored normal service.
I expected that with the module disabled, no handling would occur at all, to help troubleshooting an unrelated issue.
After a good while bouncing between different ZC versions to try and figure out why only one of three equally-configured attributes could be added to the cart, I found that the permitted attribute was the only one with a POSM model number assigned, despite the module being disabled. Deletion of the POSM entry restored normal service. I expected that with the module disabled, no handling would occur at all, to help troubleshooting an unrelated issue.