TCA9534: must configure again before writing IO

Hello,

I am using tca9534 as my IO expansion port to control a digital tube, now I have configured all the IO ports as output ports, I can set these IO ports to the number I want, I have read the datasheet of tca9534, I only need to configure the IO port once and then I can set the value. But in fact, every time I write the corresponding value, I need to configure the IO port again, may I ask why?
My understanding of normal operation looks like this:
cfg_io_as_output();
write_digital_tube(1);
write_digital_tube(2);
...
In fact:
cfg_io_as_output();
write_digital_tube(1);
cfg_io_as_output();
write_digital_tube(2);
...

Thanks.