I have never seen that because I never use a loop to attach leader to a flyline. The loops between floating and sinking portions have not exihibited that wear for me, as you also mentioned.
My preferred leader attachment method is (1) the zap-a-gap splice, then (2) nail knot.
For practice lines I do nail knot mono with a perfection loop to allow me to change the grass or street
leader to a fishing leader, hoping that the small butt loop segment has not been beat to a pulp on the pavement during demos.
But for fishing trips, I like to do a zap-a-gap splice best:
- strip .5-.75" of core
- sharpen the end of butt material w/ razor, sounds hard but it's easy
- work the butt inside the core and even into the flyline, bulge makes it evident where it is
- apply a drop of flexgap or zap-a-gap to the exposed core
- sometimes I color the core before gluing for add'l stealth
In the field I just use a nail knot directly to the leader. There are at least three ways to tie one while standing in the water without any tools, per the "Works for me" thread ongoing as we speak.