GIMP, cannot fill a circle on a background layer

Question

The canvas for my image is a rectangle no bigger than the original image. I want to put a circular background with the image. I've tried two ways:

1. I create another layer, resize it large enough for a bounding circle, and use selector to draw an ellipse. However, I can't get the paint bucket to fill the circle (it only fills to the extent of the original image - as shown in the image here).
2. I resize the existing layer and use selector to draw an ellipse. I can't get the paint bucket to fill the circle here either (same problem).

Here's an image with both a second layer and a resized original layer. How do I get the paint fill tool to add colour to the four segments of this circle so that I can get a full-circular background?

This answer seems to address the issue. Annoying GIMP issue (fill bucket with a circle-slash icon on the cursor). However, the solution presented here is not working for me.

Answer 1

This is likely because you have not ticked the Fill transparent area box.

However, since you make a selection to define the shape being filled, you should really be using the "Fill whole selection" instead of Fill similar colors. This of course fills the full circle, but if you move that layer under the layer with the house, you get the result you want, without the gaps that you can get with Fill similar colors (and you wouldn't need to add black to the layer with the house).

In other words, you generate this:

Like this: