Examples:
G2X4IA~5
O2T3KH~K
SYJ2IT~R
Solution:
The MAC user(s) in question should stop using trailing spaces and/or special characters in directory names. That's it. Almost every one of the directories in question had a trailing space, and the rest had a trailing special character (one actually had both which was a good test case). Simply removing them immediately cleared things up.
Edit /etc/smb.conf
(*) and add mangled names=no
to the [global]
section and restart the smb service.