Sorry if this has already been reported, it's a pretty old bug but I couldn't find any lists of bugs.
While inside Mo Krill's Burrow your Active Items cast is default to "Instant Cast" regardless of your keybind settings. So even if you have Active Cast set to "Item Default" or "Confirm Cast", when you use a Knockdown while Burrowed it still behaves as "Instant Cast".
Outside of Burrow it works fine.
Since this is pretty straight forward I'm not posting any clips or match IDs, but just let me know if you need it.
While inside Mo Krill's Burrow your Active Items cast is default to "Instant Cast" regardless of your keybind settings. So even if you have Active Cast set to "Item Default" or "Confirm Cast", when you use a Knockdown while Burrowed it still behaves as "Instant Cast".
Outside of Burrow it works fine.
Since this is pretty straight forward I'm not posting any clips or match IDs, but just let me know if you need it.