Actually, it seems to be a second nit that makes this extension useless on AMD for me (unless another work-around is found); The DX side doesn't seem to see updates to the resource done from the GL side. The reproduction case can trivially be extended to show this by adding animation to the GL-code in the while-loop.0
I've tried to change the access mode to read-write, ping-pong between read-write and write-discard, unregister and re-register the object, to no avail.