Correct mimetype not identified when uploading via Explorer or ftp

[Steps to reproduce]
1) Put mimetypes-extension-map.xml in extension/mimetype/
this file extends Alfresco with 3 new mime types:
∙ application/x-xmind (extension: xmind, xmap)
∙ application/vnd.mindjet.mindmanager (extension: mmap, mmp, mmpt, mmat, mmmp, mmas)
∙ application/bizagi-modeler (extension: bpm)
2)Start Alfresco
3)Send via FTP the attached files to the repository
4) Check the mimetype of the uploaded files on the details properties page on Share

[ Actual Result]
Documents have ZIP mimetype

[Expected result]
Files should have the correct mimetype

[Notes]
∙ If files are uploaded through Share the correct mimetype is visible
∙ Sending the files via FTP org.alfresco.repo.content.MimetypeMap.guessMimetype(String, ContentReader) is invoked
Possible workaround/solution -> add MediaType.APPLICATION_ZIP.equals(type) check:
// If Tika has supplied a very generic type, go with the filename one,
// as it's probably a custom Text or XML format known only to Alfresco
if (MediaType.TEXT_PLAIN.equals(type) || MediaType.APPLICATION_XML.equals(type) || MediaType.APPLICATION_ZIP.equals(type))