When you add filter condition Qtr in [ "Q1" , "Q2" ], it will make query to database and cache result with this filter condition.
Now next time when you say Qtr in [ "Q2" , "Q1" ], because of change in sequence, it doesn't understand that filter condition is matching with older one.
When you add filter condition Qtr in [ "Q1" , "Q2" ], it will make query to database and cache result with this filter condition.
Now next time when you say Qtr in [ "Q2" , "Q1" ], because of change in sequence, it doesn't understand that filter condition is matching with older one.