Thank you for your input, you've spent a lot more time staring at GF things than I have. If I understand the math correctly, it should be impossible for that case to happen. Because two different exponential functions can only cross at one point, and the faster tissues will always be ahead of the slower tissues. Of course, you'll be able to find many examples of the opposite, where first a faster tissue controls, and then a slower tissue controls.
At a stop a faster TC can off-gas "enough" while slower TC remains close to its M-value. Go up and your slower TC is controlling, until you get high enough to push the faster one closer to its M-value. I don't know what it'd take in practice for a given model, but by numbers it's perfectly fine for them to switch back and forth during ascent.