BUG? SMTP File Protection not work correct

the bug is in MTA and transparent mode.

in smtp policy i select under file protection "document files", but wen a email come with yxc.doc then no filter (doc file is a text file rename to yxc.doc)

a anoder test, i create a file type with doc extention but no work

the filter only work wenn select to "all" or "image file" , test with jpg picture is ok

FW ver. SFOS 17.1.3 mr-3