When upload documents assigned to a custom mimetype, Alfresco does recognize it as the custom mimetype, but as a normal OOTB mimetype. For example, creating a custom svs mimetype (which is essentially a tiff file) will show up after FTP upload as a tiff. Uploading this same document through Share will properly display the document as SVS.
Steps to Reproduce
1. Create a custom mimetype extension and restart Alfresco
2. Upload a document of created mimetype via Share. Verify the mimetype is correctly identified
3. Upload same document through FTP. Verify Alfresco is now showing a different incorrect mimetype
Alfresco will display the correct mimetype in both Share and FTP uploads
Alfresco will only display the correct mimetype in a Share upload