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I believe that the interface is quite safe to use. There isn't anything difficult to go wrong, because it is simply not allowed by the interface. However, there can be two places where it might be unsafe. Firstly, the user may erroneously drop something into the recycle bin and be unable to get it back. Secondly, the user may accidentally hit the back button of his browser, and lose his chosen items. This can be solved using cookies in the browser.