Why is pivot off centre?

[Winter]

I've created a ten sided Ngon and extruded it. I then applied an Edit Mesh modifier and selected the front face. So far all okay... I've then done a uniform scale and the face has a pivot point off centre, thus scaling the face off centre. I've tried to select the face and go into the Hierachy tab to centralised the pivot but it becomes unselected.

The pivot is shown in the centre until I pick a face or polygon and then it swings off centre.

I would like to resolve this instead of having to physically move the new face back to a central'ish' position.

 

Thanks....