See that ︿ above the Name column of the Document List? Like most tabular data tools (spreadsheets, or the data tables in Wikipedia, or what have you), that indicates that the data is being sorted by that column (if you right click, and add the extension column, you can sort by either column). The sort indicator is a 3-state toggle: pointing up ︿ means it’s sorting in alphabetical order, pointing down ﹀ means it’s sorting in reverse-alphabetical, and gone means it’s sorted in the order of your tabs.

up ︿ down ﹀ none 98a5bc45-296d-41cb-8baf-635e729f540f-image.png 4b34c789-9bf5-4185-8d46-eceebbf07ced-image.png 1a0eadaa-367e-4f37-a2e0-0b84748c5cb1-image.png

Nothing changed in Notepad++ itself; you just clicked that header once (intentionally or accidentally), so it’s now sorting alphabetically, like it thought you wanted. You just have to click it two more times to get it to match the tab order.