Rammus Q / Black Shield / Aatrox Q interaction

Expected behavior:

Rammus gains Black Shield Rammus rolls Aatrox Q hits Rammus Black Shield prevents the CC Roll is not interrupted

Actual behavior:

Rammus gains Black Shield Rammus rolls Aatrox Q hits Rammus Black Shield prevents the CC Roll is interrupted by attempted (but immuned) CC

This frame has the relevant information: https://puu.sh/DCs2d/58cabbe9d1.png -- Note that the Black Shield buff is still active, the CC has been immuned, but the roll buff has terminated.