Copper/Ground Fill only on ONE side?

Why is not possible to fill only one side of the pcb? or is it me? is it bad practice?

I just tried, and had no problem filling a one sided board with a ground fill on the bottom.
Can you be more specific about your need?
Is this a two sided board or one sided?
If it is supposed to be one sided, do you have the PCB specified as one sided in the inspector?
If a two sided board, which side are you trying to fill?

I just did some more experimenting and found this.
If you have a 2 sided board, and on the bottom toolbar both layers are selected.
The ‘routing/ground fill’ button will show both top and bottom ground and copper fills.
If you select on the toolbar which layer you want to fill (top or bottom),
then the ‘routing/ground fill’ button will change to show only the selected layer to fill.

i dont see an option form the menu that let me fill just one side…
is there any other way to do it?

Ohhhhhh… definitely very a counter-intuitive user interface…