Originally Posted by
Goldorak
This is done to avoid to have 2 flights the same day with the same flight number (the delayed one and the regular flight of the day).
Thanks Goldorak! ^
Then on 19th August, this was perhaps done as a precautionary measure for AF7 which departure time was initially 19:00 and became 21:45 under AF4081 (effective departure time: 22:47) - still on the same day.
For AF11, it's more obvious. Initial departure time was 21:55, rescheduled to 00:45 on Day+1 indeed as AF4085 (effective departure time: 01:40!).