I was doing some testing on singleplayer and I put 666 (don't ask why) TNT minecarts on a rail and held 1 totem of undying in each hand. Then I made them all blow up at once and after a huge BOOM I died.
I went back to the explosion site and retrieved all my items but the 2 totems were gone...
Could they have some sort of vanishing curse on them by default?