A couple of weeks ago, a bug introduced into the latest Team Fortress 2 vastly increased the drop rate of Unusual-rarity hats from loot boxes. As a result, Valve disabled item trading, so as to prevent players from accumulating a bunch of rare hats and trading or selling them for a profit.
Last week, Valve implemented a fix for the issue, as described on the TF2 blog. The first Unusual hat obtained by an account will be tradable, but any acquired after that first one will not. If you decide you don’t want to keep any of those non-tradable hats, you can receive a refund, receiving “the full price paid for any hats, crates or keys bought on the Steam Community Market or Mann Co. store.”
Valve also noted that many players who opened bugged crates and got Unusual hats might have been concerned that they would face punishment for acquiring one and thus deleted the incriminating item(s) — believing, apparently, that Valve wouldn’t possess a record of who opens and deletes everything in the game. Regardless, such worries were unfounded; “you didn’t do anything wrong,” Valve said, “so hats from bugged crates deleted before the tradable date will be restored to your accounts with the same restrictions described above.”
Full tradability and refunds will be implemented “in about a week’s time,” which should be sometime before the end of this week.