Resource leak: 'in' is never closed, though it IS closed

I know that there are a couple of similarly entitled questions out there, but most of them have simply forgotten to put a close() directive on their stream. This here is different.

Lets say I have the following minimal example:

public void test() throws IOException
{
    InputStream in;
    if( file.exists() )
    {
        in = new FileInputStream( file );
    }
    else
    {
        in = new URL( "some url" ).openStream();
    }
    in.close();
}

This give me a Resource leak: 'in' is never closed warning in Eclipse (Juno SR1). But when I move the in.close() into the conditional block, the warnings vanishes:

public void test() throws IOException
{
    InputStream in;
    if( file.exists() )
    {
        in = new GZIPInputStream( new FileInputStream( file ) );
        in.close();
    }
    else
    {
        in = new URL( "some URL" ).openStream();
    }
}

What is going on here?