silent background execute program cause Vim screen text disappear.

[stardiviner]

I write a function like this in .vimrc:

    function! VimwikiWeblinkHandler(weblink)
        let browser = 'firefox'
        execute 'silent !"'.browser.'" ' . shellescape(a:weblink, 1)
    endfunction

When I press "Enter" on the link. It will use browser firefox to open it.
But the Vim screen's text will disappear.
I made a screenshot of this. It is in attachment.
--
[ stardiviner ] ^^&^^ {I hate all of you !  Leave me alone}
IRC(freeenode): stardiviner     \\ Twitter:  @numbchild \\
GnuPG Key fingerprint
    >>> 9BAA 92BC CDDD B9EF 3B36  CB99 B8C4 B8E5 47C3 2433

<<attachment: 2012-05-26-094405_919x559_scrot.png>>

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