When trying to Save an Assembly that has a WindChill Modification Conflict with a submodel, and then setting the Action to READ ONLY, the Assembly will not be saved initially. Saving the assembly again WILL work. This is critical as users think their work is being saved initially and then they end up losing everything if they close out of Creo without saving again. The small error message is not enough. There should be a use-case scenario within the software that saves the assembly even if a submodel is set to READ ONLY.
PTC says that this is a change in behavior and thus, this improvement idea is created!