Shortcode Always Displays Default Attribute Value

Question

My shortcode always uses the default value for the single attribute, reviewstoshow, instead of the incoming attribute value. The incoming value has the correct number (per the second half of the dump included below) but the $numberofreviewstoshow var is always set to the default value (6).

Here is the shortcode being used:

[tdp_random_reviews reviewstoshow="8"]

This is the shortcode code:

add_shortcode( 'tdp_random_reviews', 'show_tdp_random_reviews' );

function show_tdp_random_reviews($atts) {
    $a = shortcode_atts( 
            array(
                'reviewstoshow' => '6'
            ), 
            $atts 
    );

var_dump($a);
var_dump($atts);

    $numberofreviewstoshow = $a['reviewstoshow'];

<snip>

}

Here is the output from the two var_dump() lines:

array(1) { ["reviewstoshow"]=> string(1) "6" }
array(1) { [0]=> string(30) "reviewstoshow="8"" }

Can you tell me where my mistake is? Thanks!

Answer 1

The quotes in the shortcode call were not standard (despite them looking so). Replacing the old double quote characters with typed-into-notepad, copied, and pasted new quotes in the theme editor resolved the problems.

Thanks to @WebElaine and @vancoder for the help!