Yesterday I accidentally clicked twice on the same invite and it said I got trinkets again. I thought perhaps it was just a bug and trinkets werent distributed so I emptied my inventory, clicked on a previously claimed invite and indeed got trinkets again. Not sure if this is a bug for everyone or just me.
Are you sure you weren't just accepting multiple invitations? The url https://subeta.net/explore/masquerade.php?act=invited&accept=accept is the universal link to accept any and all dance invitations. That page gives you the trinkets. From that page if you click "go to the dance floor", you should get a specific dance number.
Since all the events link to that universal page, you could've been clicking on the same one, but accepting multiple dances?