High ISO with Flash
I have just bought a Canon 77D and it's first use was at an daytime, indoors children's birthday party.
The camera was initially set on Auto as I hadn't had an opportunity to become familiar with it. In general the photos looked a little overexposed and I was surprised to find the camera had chosen ISO of around 3200 even though flash was used.
After this I turned flash off and the camera selected an ISO of around 600 - 800. The shots were of similar subject matter to the first set but were of much better appearance.
My question is this - why would the camera select a much higher ISO when using flash and a lower ISO when not using flash under the same photographic conditions?