"Start before Stopping" is not checked even "upgrade_strategy: start_first: true " is set in rancher-compose.yml


I’m using Rancher 1.6. I have several services that built by TeamCity and deploy to docker. In 1 service rancher-compose.yml, I set
start_first: true

The build was success and deployed. But when I open rancher UI and navigate to the service, the check box of
“Start before Stopping” is not checked. (see attachment image).

So what should I do to make checkbox “Start before Stopping” be checked by default?