Hidden tnslsnr loopback port lead to a conflict

Each listener has a defined port number. But together with this port there is always a second port used for the loopback which isn't documented at all. The listener loopback  port is assigned dynamically and therefore not under control. In our case it was in conflict with an application port leading to serious problems. Here for example a typical layout for the listener using one defined and one dynamic port:

tnslsnr   20581  orap03   12u  IPv4 0xe0000003ce5e63c0           0t0      TCP db1.test.com:listenerp03 (LISTEN)
tnslsnr   20581  orap03   13u  IPv4 0xe0000003ce490040           0t0      TCP localhost:54920 (LISTEN)

Port 54920 is a fixed port for an application which was down during the listener restart. The listener occupied this port for the loopback adapter and avoid the application working properly. Is there a way to define also the port for the listener loopback adapter? Why isn't the loopback port mentioned in the listener documentation?