Many items have charges on them but their property is single use.
Bloodgem ring
Mystics eye
(Those are the two I can think of offhand, post anymore you find, I am also assuming this is a bug)
Oh... this is more of an evolutionary vestige than a bug as when you create 150+ items, you tend to copy/paste from some template and sometimes these slips in...
It's harmless either way, but thanks for reporting.