Area Tool Only Works Once

I'm using Acrobat Pro Ver 7.1 and Windows XP, SP3. This is a new laptop so I migrated the installation over from the crashed hard drive of my previous laptop.

I used the Area Tool to measure a building on a drawing. First I took a measurement of a known distance and set the options to "5 in = 11.25 ft".

I then proceeded to measure the area of the building. The area was displayed correctly and the "Area" lines remained on the page.

I then when to measure another building on the same page. The "Option" window displayed the measurement correctly, but when I closed the "Option" window, the area lines for my second building disappeared.

While holding my mouse over the 1st building I discovered that it seemed to copy and past the previous measurement over the previous building rather than give me the new values for the 2nd building and leaving the area on the page.

My options for the tool are set to:
- Show Details, Checked
- Snap to 2D Content, Checked
- Snap to 3D Content, Checked

--2D Measuring
- Use Scale and Units from Document (when present), Checked

--2D Snap Settings
- Snap to 2D Content, Checked
- Snap to Paths, Checked
- Snap to Path Endpoints, Checked
- Sensitivity: 10 pixels

--3D Measuring
- Use Scale and Units from Document (when present), Checked
- Use default display unit: Inches, Checked
- 3D Measuring Mode: Auto

--3D Snap Settings
- Snap to 3D Content, Checked
- Snap to Points, Checked
- Snap to Arcs, Checked
- Snap to Edges, Checked
- Sensitivity: 10 pixels

Any Idea what's wrong?
Regards,
Dan