Performed more investigation and found out, that it works even strangely, than I thought:
When I give the item to an enemy:
give item _cloak_ to _mage_
and then kill it and take the item from its body, it behaves just as described above: could be used only when I don't wear it.
But when I give it to PC:
get item _cloak_
,
It behaves differently:
It cannot be used at all, but when I wear it with
Equip button,
_adjust_ action triggered, just like it was used!
Another interesting thing is that if I use it as described above (with
use command) and it displays a message in
_adjust_ action, I leave inventory mode. But if it is used the second way (with
Equip command), after message is displayed, I'm back in my inventory. And if the action puts an item to the inventory, like this:
_adjust_ task:
say 1083
get item _map_
,
it do not appear before I leave inventory manually and then switch back to it!
So, this strange behavior seems to be obviously a bug.