Skarner ult + Auto Attack interaction

Not entirely sure whether it's a bug error or a Quality of Life change that hasn't happen but whenever Skarner uses his R "Impale" and suppresses his target, even though he can move and use all of his other abilities, he can not auto attack his suppressed target. He has the ability to auto attack other enemies, units, or neutral monsters but not the target being suppressed. There is no information on this interaction so I was not sure whether or not this was a bug that has been occurring for the past few years and not reported or if this was a quality of life change that has not or will not be changed. Please do either look into this or explain in full detail how this ultimate interacts with the rest of Skarner's kit.

Thank you