Right, I also claim this happens[1], but my observation is that the background thinking only reliably seems to resolve when you step into the metaphorical shower. If you stay deeply focused on something else instead, the background processing seems to be supplanted with thoughts about the new problem. It's in fact the main reason why I put so much emphasis on stepping away from the work. Whenever I do I come away with a long list of solutions, often at a pace where I'm barely able to write them down before the next one arrives.