Maximum Fuel Transfer Weight

[tdracer]

OK, so I'm reviewing a 747-8 AFM revision (something I periodically need to do as part of my job) when, on the Weight Limitations page, I notice something called:
Maximum Fuel Transfer Weight (MFTW)
Now, being an engine guy, I'm not normally concerned with the Weight Limitations page (I only noticed as it was a revised page), but that entry perked my curiosity. What does "Maximum Fuel Transfer Weight" really mean?

TIA

[B-HKD]

The limit is due to wing stress and load relief. Transferring fuel from the reserve to main tanks, happens automatically under normal conditions,however non-normal's may required a earlier transfer hence the limit to protect the wing/structure.

Strangely I have seen -400 FCOMs with it, and others without it. May have had something to do with the engine type on the -400.