Problem with Google Drive API File Sharing - Commenter ("additional role") no longer works

[Tobin Henninger]

A month or so ago I was able to set permissions on a google file to share it with another google account, and I added the permission with an authenticated request like this:

service.Permissions.Insert(new Google.Apis.Drive.v2.Data.Permission() { Value = user.EMail, Type = "user", Role = "reader", AdditionalRoles = new List<string>() { "commenter" } }, file.Id)

It worked fine...until today. Today I get the following response:
Bad Request. User message: "Sorry, an item is restricted in sharing."

Even when I try to use their demo I get the same response:

https://developers.google.com/drive/v2/reference/permissions/insert

The only posts I've seen about this were from years ago, so I wonder if they accidentally broke the API for the commenter role.