Freaking Nasty UnitDropItem Bug

=.=...
This bug, owned me hard. But well, at least I found it.
Test Map:
- Keep using the item in the third slot of the Paladin

Each time a spell "starts its effects", it will display the ability name. (Either Roar or Howl)
Each time an item is used, it will UnitDropItem the item into the first slot (0) and diplays a "Used", thus swapping the items' slot positions.
The initial item in the first slot is Roar, the one in the third slot is Howl.
Now that you used the third slot item aka Howl, Paladin will cast Howl and the Howl-Item would UnitDropItem to the first slot, thus swapping the slot positions.
No problems so far, but if you now use the third slot item again, and this time it's Roar, it will display some crazy stuff:
Both Roar and Howl were cast, only Roar was used though.
Then again, if you use the third slot item for the third time, and this time its Howl again, it would display the usual thing.
This is just so random that I failed at trying to give a description for this freaking bug while posting, =.=>

Without really looking at the map, I'd hazard a guess at the fact that it's the orderids doing something. When you order a unit to use an item, it is issued an orderid corresponding to the slot of the item. Switching the items might cause both to be triggered by this slot orderid in some way.

Well, if that was true, why won't it cast both spells if you reuse the first item again? Also, dropping the item manually won't have that side-effect.