This issue is about the third case in this method called with the model for a managed server entry:

bool
NetconfAgent::checkModule(const string& module_name) const {
    if (module_name.empty()) {
	return (true);
    }
    auto module = modules_.find(module_name);
    if (module == modules_.end()) {
        LOG_ERROR(netconf_logger, NETCONF_MODULE_MISSING_ERR)
            .arg(module_name);
        return (false);
    }
    auto modrev = YANG_REVISIONS.find(module_name);
    if (modrev == YANG_REVISIONS.end()) {
        // Can't check revision?!                                               
        // It can happen only with a module which is not in                     
        // YANG_REVISIONS but installed so likely on purpose.                   
        return (true);
    }
    if (modrev->second != module->second) {
        LOG_ERROR(netconf_logger, NETCONF_MODULE_REVISION_ERR)
            .arg(module_name)
            .arg(modrev->second)
            .arg(module->second);
	return (false);
    }
    return (true);
}

Tomek requested a warning, I added the comment after Can't check revision?! and answered:

No warning. In fact it means the module is installed but is not in yang revisions so either it is on purpose and the check was simply disabled, or it is a real error and the translator will raise a better error.

I am creating an issue in the case a better option could be found.