A setting of 9 causes the Inverter to be initialized in 3-wire sequence mode. When the setting is changed to 9 and the Return Key is pressed, the Inverter is immediately initialized. At this point, the n01 setting is also initialized and reverts to its default setting of 1.
The same phenomenon occurs if the setting is changed to 8.
Think of parameter n01 as a command that initializes the other parameters. Because it is a command, it does not retain its setting like a parameter.
It is normal for n01 to revert to a setting of 1 after initialization.