Urgot Ult: More clarity needed for what is 25% hp for unique hp bar champs and a question for Riot

Urgot's new ult for those who haven't seen it yet is an execute that is able to be activated after casting if the target below 25% hp and can act as an up to 75% slow if they aren't meeting the 25% hp minimum. His ult says his targets health has to be 25% which is pretty straight forward for anyone with single hp bars but what's the game clarity behind Kled who has 2 hp bars? Does 25% of target hp in that sense then become just Kled's hp or is there the wiggle room of kled and skarls combined hp? I ask this because apparently even if the total hp amounts to below 25%, the ult can not be reacctivated at all until he is unmounted from his mount. Is this a game bug that hasn't been addressed yet or reported ? or was the ult not really checked out clearly for the uniqueness of Kled duo hp bars. How would this address over to hp shields like Tahm Kench's also?

Would love your answers and comments on this and what you think.