Each instance of Experienced can only be claimed once per character, but you may have more than one (I have 3 on my account, for example due to various Rewards). They stack, so you can have a 10 or 15-use "version" of the power in your tray and any subsequently claimed instances will add to that.
It sounds like you've got 2 (It should actually give you the number available listed in the mailbox when you go to claim it).
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One of the Paragon Rewards Tier 7 choices gives you a power called Experienced. Claiming the power from the Account Claim tab of the Email window creates a temporary power in your Powers window called Experienced, which gives half a level's worth of Patrol XP each time it is clicked, up to 5 uses. Once the power is used for the 5th time, it disappears from the Powers window.
The perk does not get removed from the Account tab of the Email window, however, and can thus be claimed multiple times.
The problem seems to be that if you claim it once, and then claim it again before the initial 5 charges are used, the perk then disappears from the Account tab of the Email window and can no longer be claimed.
If the perk can be claimed multiple times for each character (as seems to be the case from the current implementation), is there a way to trigger the perk to appear in the Account tab of the Email window? Can I put in a support ticket to have this fixed?
Or is the issue that the perk should only be claimed once per character?