It was 99.9% obvious that this is an unintended Bug but I understand how Tarsq came to his conclusion. Imo it was avoidable by Byte, if he explained that Tarsqs conclusion (95 ISS -> 104 ISS works so 104 ISS -> 95 ISS should work, too) while correct is not what will be fixed, but the assumption itself.
Either way, Warden having 15% Atkspeed twice is not op at all because even before fix, both ISS had shared Cooldown of 8 Seconds. So even if it got "fixed" to Tarsqs expectation, you use 104 ISS, wait 8 second, use 95 ISS and get 15% Atkspeed again with 50% Chance. Now you only have 7 seconds left of the first 15 % Atkspeed and 15 second of the new 15% Atkspeed. If we were talking about Rogue/Warlock or if it was 15% PDMG instead, then yes, that would be op. So I think it is a bit too much to compare that to 50000% dps skill on knight.
Tbh I am more surprised by how quick the unintended bug got fixed. Gj devs