More weirdness - widgets disappear when adding a body background

Installed GP on another site today, activated premium and set about customising it. Decided to add a body background with the customiser, the preview showed all the right side widgets had gone. Thought it was a customiser bug, published anyway and sure enough when I went to the site, all the widget entries had gone for the sidebar?

Really?

If I revert back to the previous theme the widgets get restored, if I then activate GP the widgets are back. Soon as I change background though they're gone.