I find that pasting with the middle mouse button in notepadqq pastes the contents of the clipboard, not the last selected text like in other apps. Its been reported; https://github.com/notepadqq/notepadqq/issues/456
And there is a suggestion that it may be tweakable from outside notepadqq, but since other apps work as expected, i'm sceptical that it can be addressed that way. Any ideas?