I can confirm the issue.

I have tested on Ubuntu 16.04.2 and 17.04. Both give the same results.
17.04 as of today uses kernel 4.10.0-33-generic #37-Ubuntu.

I am using Radeon Rx470 for testing.

I can successfully overclock memory on Windows.

Many other people have this issue on amd.com and phoronix.com forums.

I do not believe I have run across a single instance of this working across
many forums where I have investigated.

I am willing to provide further info and testing if required, and have placed
myself on CC.

Thanks,
Vittorio