For those interested, this turns out to be a server-side problem.
Converting the email to a readable image is a compute-intensive task, and apparently, the time it takes for the email to be converted to an image is too long for the webserver serving the page, so it fails to load the email image and just displays the Invalid Hash message (I assume this is a default image).
You can generally get the email to display correctly by refreshing the page (or better forcing a reload).
The problem is worst with a page with multiple email addresses - often only the first few will load, and the rest fail.
But refresh will usually get the desired result - eventually.
There is no plan to modify anything, as there are ways of getting at the email address (mentioned in this thread), and its primary function is fulfilled - preventing spambots from harvesting addresses.
SD