Users suddenly missing write permissions to the root drive c within an active directory domain

Solution 1:

I'm not allowed to comment yet and this isn't a solution as such, but I have noted the same sort of behavior on Windows 7 and 8 in addition to Server 2012 and Server 2012 R2. On top of that, this happens from the Administrator account even after changing the ownership and full permissions of the drives root directory to the Administrator account. Also, this experience was observed on the local account with machines in a workgroup, so networking and the being in a domain is not part of the issue.

For example, Administrator is not allowed to copy a file from the D: drive to the E:\ root, but can copy to E:\temp and then move the file to E:\. Copying is not allowed, but moving on the same drive is.

If you really have users that are allowed to do these functions:

Some users (not all!) report that they cannot any longer save, copy or write files to the root drive c

I would suggest studying closely what is unique about their accounts compared to the others. As far as why the behavior changed, I just assumed that it was something that got applied with Microsoft update. (Sort of an answer :-)