IBM ICN is no longer setting the default0 mimetype header of 'application/octet-stream' when calling p8/additem from a Entry Template

Question

When adding a document from a IBM ICN Entry Template for file types defined in the windows registry the call to p8/additem has the header field mimetype and correctly sets the MimeType as showen in this Chrome debug session with a PDF file:

However, if I add a file such as XYZ that is not defined in my windows registry it use to add the header to the call with 'application/octet-stream' but now the header is just not there unless I add .XYZ to the windows registry:

Any ideas what could have changed that it no longer defaults that as we have a plugin looking for that value?