Dup bars show atmo O2 level when suit unequipped

Does this happen when the dupe removes the suit at a checkpoint, when you manually remove the suit, or when the dupe drops the suit after it has run out of oxygen, without going through a checkpoint?

Manually removed, not a checkpoint.

From my experience, dups do not drop the suit when it runs out of O2, they just pull off the helmet to breathe, then put helm back on and continue.