Unable to right-align view using contraints

Unable to right-align view using contraints

I have a tableview that uses a custom UITableViewCell. The cell contains a
UILabel that needs to be right-aligned in the cell.
This is an iPad app. I've designed the custom cell to fit in portrait
orientation by default (768 width). The issue is when the app rotates to
landscape orientation that the UILabel does not stay on the right side.
I've even tested to ensure that the cell itself is stretching correctly to
the width of the landscape orientation.
No matter what I do it seems that it wants to align relative to the left
side only. In the constraints in IB I select "Trailing Space to Superview"
but it doesn't seem to do anything. IB automatically sets Horizontal Space
(651) as offset from the left side. I am unable to delete this constraint.
Is this really that difficult to do or I am just missing something really
obvious?