Tixx is greedy.
When I did it, the chest opened automatically and the items were put directly into my inventory. If you were facing the wrong way, maybe you didn’t see the chest open. Check the inventory of the character who first spoke with him and see if you have anything you didn’t have before.
I’ve checked them all, none of them have it
Please, I am having this same problem. I (accidentally?) talked to Tixx in Heart of the Mists. When I didn’t get a present or anything of any sort, I figured it was because I talked to him in the wrong place, but when I went to Lion’s Arch and tried to talk to Tixx, he said I’d already got my gift. The chest is open and I’m not able to select it. I hope something can be done about this. I would really like to get a present since everybody else gets one.