When launching a fresh instance of Notepad++ it creates a tab for 'new 0'. You can then create tabs for 'new 1', 'new 2', etc. If you close 'new 1' and 'new 2' and then create a new tab, it'll use the lowest possible number that's not already open, so in this example it'll recreate 'new 1'.

But if you close all the 'new x' tabs, and then create a new tab, it starts from 'new 1', i.e. it never tries to use 'new 0'. The only time 'new 0' is created is at initial startup. This can't be right. Either Notepad++ should start counting at 0 or at 1. Not sometimes at 0 and other times at 1.