I agree that this is a bug. However, I want to point out that this usage of Except does not seem to be allowed in older versions.

In version 9.0:

We don't get the expected True answer. An error message is issued. The error message is also given for your example.

In version 10.0:

The error is not shown for your example in verson 10.0.2.

In version 10.3.1 everything works fine:

It seems that this usage of Except is new in 10.1, 10.2 or 10.3 and that the renaming rules were not yet updated to be compatible with it. With this context, it seems like a bug.

The change is not mentioned on the documentation page of Except, which is annoying.

I agree that this is a bug. However, I want to point out that this usage of Except does not seem to be allowed in older versions.

In version 9.0:

We don't get the expected True answer. An error message is issued. The error message is also triggered by your example.

In version 10.0:

The error is not triggered by your example in version 10.0.2. (It is triggered by other similar examples such as the MatchQ above.)

In version 10.3.1 everything works fine:

It seems that this usage of Except is new in 10.1, 10.2 or 10.3 and that the renaming rules were not yet updated to be compatible with it. With this context, it seems like a bug.

The change is not mentioned on the documentation page of Except, which is annoying.