I think we have to look at that in its context. He was supposing this as a method of personal inquiry for impermanence.
The Buddha is just asking us to look and see “at this one time, I was feeling pain, but at the other time, I was feeling pleasure, there was no pain at that time, so clearly my feelings completely transform from one thing to another, so they are impermanent, and not worth holding on to.”
What immediately follows the quote about feelings is this:
Pleasant, painful, and neutral feelings are impermanent, conditioned, dependently originated, liable to end, vanish, fade away, and cease.
Seeing this, a learned noble disciple grows disillusioned with pleasant, painful, and neutral feelings. Being disillusioned, desire fades away. When desire fades away they’re freed. When they’re freed, they know they’re freed.
I believe this is the extent of the purpose of him mentioning this principle, it isn’t to lay out a universal, philosophical principle that makes sense in every context. This is also typical of the MN suttas which tend to dive a little further than most know into specific topics.
Even The Buddha said that he does this in MN59:5.2
Ānanda, the explanation by the mendicant Udāyī, which the chamberlain Pañcakaṅga didn’t agree with, was quite correct. But the explanation by Pañcakaṅga, which Udāyī didn’t agree with, was also quite correct. In one explanation I’ve spoken of two feelings. In another explanation I’ve spoken of three feelings, or five, six, eighteen, thirty-six, or a hundred and eight feelings. I’ve explained the teaching in all these different ways.
Let’s use this model and say feelings can happen at the same time in all the ways people in this thread have cited. When they change altogether from both tasting cake and shame to spiritual pleasure and back pain, clearly feelings are still impermanent. When you focus on one part of your vision, but the peripheral areas are still sensing, both these areas are still subject to impermanence, which is within the bounds of the main point of the original quote. What really matters is whether you hold on to feelings, believing that they will last. Finding technical logical contradictions whether philosophically or in meditation experience is drawing away from the point, which you could see as a small reflection or explanation that he made for the sake of helping the audience see the direction of the path to awakening.