Pending, at the top of your dashboard's sidebar, lists the discussions that need your team's attention: new requests and new replies from customers. Discussions started by your own support staff (the site owner included) don't go there, whether they were written on the site or sent by email. You wrote them, so Tender assumes you already know about them. They're under All.
So if you test your site or your email forwarding from your own address, the discussion seems to vanish. Test from an email address that doesn't belong to anyone on your support team, such as a personal address, and it shows up in Pending.
The same thing happens when you forward a customer's email and Tender doesn't recognise it as a forward: it's posted as yours, and lands in All rather than Pending. See Forwarding emails from customers to Tender.
If an email doesn't show up anywhere, see Troubleshooting & Heartbeats.