Trying the native Mac OS version worked, but the one installed by MacPorts (/opt/local/bin/file) would just report a regex error.
$ /usr/bin/file magicmagic: magic text file for file(1) cmd$ /opt/local/bin/file magicmagic: ERROR: line 19439: regex error 17, (illegal byte sequence)
A closer look at the magic file that lives in /opt/local/share/misc/ revealed that line 19439 is
0 regex/s \\`(\r\n|;|[|\xFF\xFE)
Disabling the line with a "#" and recompiling the magic file with the "-C -m <magic file>" solved the issue.