Hello. We ended up replacing the pn.php file with the script you provided. It solved one problem and created a new one.
1. Replacing the script does allow you to see all of the Pinterest boards in the list box BUT –>
2. If you select a particular Pinterest board and then update the post, the Pinterest board reverts to the default Pinterest board. In other words, you can’t pick a Pinterest board for a post, other than the default board.
The new pn.php script doesn’t seem to fix that problem.