shadowbox fails on links that include slugified image filenames

In our CMS, we are using links such as

http://localhost:59744/Admin/ContentPage/EditAttachment/31/Hydrangeas-jpg

to edit an attachment to the content of type ContentPage where 31 indicates the content ID and Hydrangeas-jpg indicates the slugified filename that is attached. This link will display a form that allows editing/replacing the attached file. The response from the server works fine (if opened by browsing directly to the URL). However, if including this URL in a link with Shadowbox attached to that link, the Shadowbox will open partially then start loading and never completely open and load the link.

This only happens when the link contains "-jpg", "-gif" or "-png", so for the image extensions only. I guess it must be detecting that we are trying to open an image (while we don't, we want to open the HTML page) because it is working for "-pdf".

At first I thought the dash "-" was the problem but then figured out that it works perfectly for instance for

http://localhost:59744/Admin/ContentPage/EditAttachment/31/leaflet-pdf

Hopefully you will be able to reproduce and fix this. Thank you for a great product.

Reproduce the issue with the ContentPage edit URL ending in -jpg, -gif, or -png, comparing it with the working -pdf URL. Start by tracing Shadowbox's link-type detection and loading behavior; done means these URLs open their HTML form completely instead of being treated as images.