i allways played it this way, but in the rules (page 18) it's written that both player could attach the same enchantment to an object (no mention of revealed or hidden)...
hence, as i read it, a player could cast the same enchantment as an opponent's revealed enchantment. the new enchantment would be destroyed when revealed, but it can be useful as a bluff.
I am guessing that you are mentioning this:
<begin quote>
Enchantments are “attached” to their targets. There is no limit to the number of different enchantments that can be attached to an object or zone. However, there can never be more than one revealed enchantment with the same name attached to the same object or zone at the same time. Also,
you cannot attach a second hidden enchantment that has the same name to an object or zone that
you have already attached a matching enchantment to, whether revealed or hidden. For example, there cannot be two Wolf Fury enchantments attached to your creature.
<end quote>
It appears that this takes care of the following:
Multiple enchantments of different names, either revealed or not, by either or both players
Multiple revealed enchantments of the same name by either or both players
Multiple enchantments of the same name by one player, one of which must be hidden due to the point above
(due to the use of my bold-faced "you" words)
What it apparently does not forbid (as written) is one hidden enchantment of the same name as a revealed or hidden enchantment attached by the other player.
However, the example provided seems to exclude two of the same enchantments attached by one or both players, whether revealed or not... which would cover this apparent oversight in the detail before the example.
It could be more clearly written, but I think that the example is enough to better understand the intent.