Often what starts as a little problem has a way of growing. What I found out today, it’s not only newer kernels I build but also the kernels that exist in any non Redhat 6 based Linux, so idmapd is not working properly on Centos7, Scientif7, Fedora, Debian, Mint, or Ubuntu. Oddly, an actual operation on a file seems to work correctly, if I su to a user and touch to create a file, then go back and look at it on the server, it is created with the proper UID even though it isn’t displayed correctly with ls on the client. This is why the problem has essentially gone unnoticed for so long.
As near as I can tell there is some fundamentally different way that idmapd works under RedHat 6, then any other Linux distribution or even later versions of Redhat. I’ve found copious documentation of this bug but no fix that actually works except to revert to NFSv3. The problem with NFSv3, it does not have mandatory locking that works.