Browser Fill issue with Muse CC 2014

I'm setting up a new test site in Muse. When I select Browser Fill (whether it’s a Solid, a Gradient or an Image), the colour or image fills the page content area, not the background.

When viewing the site in Preview or Preview Page in Browser, the colour or image fills the whole area (both the page content and the background fill).

I’ve checked with a test with the earlier version (CC) and that still works correctly, with the fill on the background only.

Any thoughts welcome!

(OS 10.9.3)