qgis - Problems printing OpenLayers Plugin Maps To Scale

In the print composer I can print all maps to scale and satisfactory.
However, when I add the OpenLayers, usually Bing Aerial, to the project I cannot print it out to scale. I click the scale box, set it to the relevant scale.

The image below is a section of the actual size with OS mapping:

The next image is with the OpenLayers.

Both images cropped to remove client info. It is almost double the size but in-between scales. Is there any way to correct this?

Using Windows 7, QGIS 1.8.0.