Show Label column missing in Text Field??

Insert Text Field tool, I wish to turn off the Label (mm) when I select the length of a line element.

But I can't see the column that allows you to turn off the unit labelling for Lines?

It is there when I use an Area of an element. But not for lines??

Is this supposed to be the way it is? Known bug?

AECOsim BD 8.11.9.376.