|Thanks for that test. I did the same test with the same results. Yet, the reverting happens. Not right away but after 1 or 2 hours of Excel use. |
As far as your question goes: I always set the calculation to automatic as soon as I found it was manual. I never set it to manual myself. After that these files are saved. I have to assume they are set to automatic when I reopen them. But I have not checked that systematically.
I have come up with another hypothesis: an interference with addons. I need to check with our IT guys who may have installed something that I am not aware of. I appreciate your help sofar and I will keep you updated if I find out more.
At least I have not found any clues that Excel has a hidden (registry) tweak that would switch calculation to manual if the files are (getting) too big. Or...?