No problem hope it turns out to be your problem right enough and you can sort it.

If your using the tungsten set up alone (as in without CT filters) you'll probably want to close the curtains or your light will just mix again. It will be a more stable mix than previously due to one of the sources having become a stable source but the natural sky still isn't that stable. Especially with the clouds, which may have been your 20 seconds thing.

Good luck.

David.