Event Deck Override

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Dobby
Dobby Posts: 161 Tile Toppler
I am unable to overwrite an (already saved) Event deck with a preconstructed deck. I tap on the precon, tap on the 'transfer to Event deck' icon, tap on the Event deck as directed by the UI, a popup comes up headed 'Event Deck Override', to which I tap the 'Confirm' option, but the Event deck is not overwritten.