How to stop ssh sessions being killed when doing a commit with a custom ssh service

To resolve problems with ssh sessions being expired prematurely by the SRX, I created my own ssh application like this;

# show applications application my-ssh

application-protocol ssh;
protocol tcp;
destination-port 22;
inactivity-timeout 43200;

However when I use this and not junos-ssh, I find that ssh sessions are removed from the session table when I do a "commit". How do I know they are removed from the session table? The ssh into the firewall locks up. The same also happens to all other ssh sessions.

Two questions.

1) How can I change the idle timeout for junos-ssh?

2) How do I get sessions for my-ssh to persist in the session table across a commit?

SRX320, JunOS 15.1DX49-220.