I've been using the gradient tool to horizontally fade some images to transparent in Gimp v2.8.14.
I just select the layer that I want to fade (usually it's the only layer in the image), select the gradient tool with mode:normal, opacity:100, gradient:FG to Transparent, shape:linear, repeat:none and drag a line from one end of the image to another.
It's been working fine, and now suddenly it's stopped working. When I drag the line across the image now, it always fades to the foreground color instead of transparency. If I hide the layer from the layers panel, the image disappears and shows the checkered transparency panel underneath, so there's definitely no foreground layer hiding under it.