Flash and high iso...

In P mode, obviously when taking photos in low light one's iso climbs to say 1600 or 3200 or whatever, my problem is that in these situations when I pop up the flash the iso still reads 1600 or 3200 or whatever, surely with the flash lighting the scene when the photo is taken the the iso shoot drop way down, but it doesn't, so I find myself each time when using flash having to first go and take auto iso off (to avoid high iso's in low light conditions) and then dial in a lower iso, so tedious though.

I would have thought the camera would know that using the flash in the shot to come would not necessitate such a high iso... or am I missing something? or does the cam adjust the iso just prior to the shot? cos in the reading on the screen is 1600 or 3200 or whatever but that's before it fires the shot (and flash)...maybe the 3200 is cos that's the light measurement prior to flash but as the flash goes off maybe the iso then drops for the shot itself.. any insight would be appreciated thanks.

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Jostian