Screenshot or image:
What you were expecting to happen, and what actually happened:
I was expecting that casting a One-Time spell would disable that spell for all duplicate troops within the team. The Blessed second Great Maw actually retained the ability to cast its spell, likely due to Blessed incorrectly preventing the debuff to get applied.
How often does this happen? When did it begin happening?
Likely ever since the Blessed status effect was introduced.
Steps to make it happen again
Buy enough shop tiers within the current Dervish class event so all troops start out Blessed. Put two Great Maw into your team. Cast the spell of the first Great Maw. If the second Great Maw is still Blessed, its spell will not get disabled.
Extracted from (Not a Bug) Casting one Great Maw disables my second one where this issue was identified.