I can't find a Boeing reference, but I would guess it is because LVL CHG will not command a level acceleration segment but up to a 500fpm climb at least (watching acceleration two engines when cleaning up &c.)
But is this correct or rumour? Is it a problem? I notice, in the sim, that with an assumed temp takeoff, where minimum thrust is used for the weight, that for SE acceleration at MFRA the FD (TOGA) gives level flight. Now use greater than necessary thrust and you see a slight climb depending on the surplus thrust. I was always told (true or not?) that 0-200fpm was acceptable in the calculation.
Denti, for an EU operator, is allowed to use autopilot for SE flap retraction. Therefore it is approved by XAA's. It is allowed by Boeing. All I'm trying to understand is why it is taught by some that it is forbidden when that seems not to be correct.
This links to the topic about lack of knowledge of a/c systems especially in AB's and confusion amongst pilots. Many believe their SOP is gospel; but now we learn other colleagues are taught differently and use the systems within their design parameters. IMHO there is too much blinkered training and not enough general training. Is it healthy that crews are taught only a very restrictive method of operating their a/c? Why are they not taught the design parameters and then SOP's?