Limited use items have a chance of disappearing with every use. In BT2 and BT3 you can see how many charges they have left, but in BT1 I believe it's just a percentage chance - so sometimes a Fire Horn will last for ages, and sometimes you're just unlucky and it disappears after a couple of uses. Ideally you want to have your bard carrying a couple of them for exactly this reason (or, failing that, a backup of the bard who came with *ATEAM who you can swap in long enough to steal his Fire Horn. Again.)
For BT1 on the CBM64 the chance for degradable items is 1/64 per use. It can last forever or vanish on first use, depending on your luck for that 1 in 64 chance.
I'm playing on the iPad. I saw a post that said if you sell the item to Garth's Store and buy it back it will be recharged. Do you know if this is true?