Problem pictures display in tableview

I download asynchronously some pictures and store them in an NSMutableDict开发者_JS百科onnary with picture URL as key (to avoid to download two times the same picture).

After I try to display these pictures in a tableView but when I display the same picture two times the first one is removed!

I really don't understand why?

Please help, that make me crazy!

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I used AsiHttpRequest and know i works very well.

allseeing-i.com/ASIHTTPRequest