I'm using my Mac (OS X 10.6.8), the latest application (1.3.2). It lets me overwrite when I load the preset from either the Algorithms or Presets tab at the bottom. I've just tested this, and I see the prepended U name and can edit and save with no prompts to rename. But if I load the preset via the Preset Lists tab, tweak it, and try to save it (with the assumption that this changed preset will also populate the Preset List from which I've navigated), it prompts me as stated in the original post. I see that the prepended letter is no longer U, but an L.