I've tested it over and over and it's definitely what it is. when you reply to emails, in gmail, in PD they appear when i'm in the inbox view. That simply doesn't make any sense. i reported it multiple times and it was brought up as an "intended feature". That can't make any sense. Please correct it. Just review it, use PD mail feature as a user and you will see how it doesn't make any sense. It has nothing to do with cookies, or refreshes pages. Just use it yourself enough to see how it works.
Start reading labels properly from gmail. If it's archived, it's archived, that's all there's to it.
Sent items truly show sent items, but inbox, shows everything, even items that are not in inbox, in other labels, anything that was filtered in gmail to bypass the inbox.