No that’s most likely not a bug, Ctrl+i inverts the current layer only.
And the image suggests you had moved part of the layer, leaving a transparent area (a hole basically) where the canvas background shows through, which you obviously set to white.
This is why it’s a good idea to set the background as raster layer, not canvas colour. That way, if you make a ‘hole’ in the backround layer, you’ll see the checkerboard pattern which lets you know what you’ve done.
What do you see if you turn off the visibility of that single ‘Background’ layer’?
If you see white then the suggestion by @Lynx3d is correct.
Also, I’ve tried this and there is not a bug with Ctrl+I.
I can simulate what you see by making a ‘hole’ in the ‘Background’ layer after creating an image with background as white canvas colour.
I notice you were using the selection tool. Did you accidentally delete or move a small rectangular selection?