output in custom module is not visible

[tobip]

I have this custom module where the exec command should print one line per second:

    "custom/diskio": {
    	"format": " D {} ",
    	"exec": "dstat -d --nocolor | awk '{print $1,$2}'"
    },

It works in the shell, but it doesn't show anything in the waybar.

Changing the module to this is a not very satisfying workaround:

    "custom/diskio": {
    	"format": " D {} ",
    	"exec": "dstat -d --nocolor 1 2 | awk '{print $1,$2}'",
    	"restart-interval": 1
    },

Do I have to change the way I wrote the module or is it an issue in waybar?