I'll third that.
I often put films in my EOS 3, rate them to 1 or 2 stops higher, shoot a few shots, then sometimes do a mid-roll-rewind to swap to another film. I always remember to write on the canister what frame I'm up to, and the speed i shot it at, but then when I put it back in the camera for more shots I remember to get the frame count back up, but completely forget to re-set the ISO to whatever I was using before and it goes back to DX-set box speed (hey, I can only remember one number at once).
(yes, there's probably a custom-function to tell the EOS 3 to ignore the DX-code, but i'm too lazy to find my manual and set it. It's easier to tell Ilford what to do...)