I have used the L and XL Makapuus a lot. The XL are a bit floppier but I think it is balanced thrustwise with the L because the surface area is much greater. The XL is floppy and big, they even can get a bend in them that will not straighten out which is very different than the board like stiffness of the L. They just take a little getting used to but they are good fins, just different.
Again it is perfectly normal, that is just how the XL is.
Oooh thanks good to know, that's one thing I was trying to judge, I can still catch waves with them but I felt like i was just windmilling my feet and not getting any purchase -- I am pretty seriously considering the reinforcing rods thing to give it at least a little more stiffness.