Whatever WP function assembles the $att array from the [myShortcode att1="..." att2="..." ...] string uses the " character to delimit the data. However, the “ and the ” characters seem to be read as text, not delimeters; and their use in place of " can lead to shortcode errors.
In theory, there shouldn't ever be a problem because “ and ” are not characters on the qwerty keyboard, and so would not be encountered with manual entry. Yet, cutting and pasting from sources that use “ and ” allow for their inclusion (and there should be error checking for that situation). For example, the page The Beginner’s Guide to Writing Your Own Custom Shortcode says that [helloworld name=”Bob”] outputs Hello Bob!, which is not the case because the webpage cutely styled " into ”. Cutting and pasting [helloworld name=”Bob”] outputs Hello ”Bob”!; and [helloworld name=”Bob Smith”] outputs Hello ”Bob!, since the space between Bob and Smith is read as a delimeter and the array says that [name] = "Bob and that [0] = Smith.
Doing a preg_replace on the shortcode string before it is parsed into the $atts array seems like the best way to prevent errors. The question is where to do that.
