why when i tribute my face down peten the dark clown for tribute summon,peten the dark clown effect didn't active?

in this link it said that tribute included in send to the graveyard
http://yugioh.wikia.com/wiki/Send 

sorry for my bad grammar

why when i tribute my face down peten the dark clown as a tribute summon,peten the dark clown effect didn't active?

in this link it said that tribute included in send to the graveyard
http://yugioh.wikia.com/wiki/Send 

sorry for my bad grammar

Bug? Post this in Card Rulings/ Bugs.

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If "Peten the Dark Clown" is Tributed for a Tribute Summon, the last thing that happened was that a monster was Summoned, so the effect of "Peten" does not activate.
This is because you first Tribute "Peten the Dark Clown" as a cost, and afterwards the other monster is successfully Tribute Summoned. The last thing to happen was not "Peten the Dark Clown" being sent to the Graveyard, so it misses the timing.

http://yugioh.wikia.com/wiki/Missing_the_timing 

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