When editing a class' smart parameters an array's Default Value will come out in a format quoted in a way that does not allow the smart parameters to be saved without manual intervention.

Example:

Using the snmp class, editing the agentaddress variable Foreman presents the Default Value as "[\"0.0.0.0\"]" . However, when trying to save the form this error message pops up: "The class could not be saved because of an error in one of the class parameters."

Upon editing the value to ["0.0.0.0"] one is able to save the form. The other problem is you have to edit ALL the parameters that are arrays.

Same problem with all other classes I checked, so a general error not only related to the snmp class.