The winter leaves, being more succulent, have more stored reserves for
supporting a new bud. The winter leaves are also less likely to rot
since they are designed to last through a cold, dark and damp winter.
Also when winter leaves are taken, the plant quickly fills in the
damage with new, bigger spring leaves.
Judging by how easy it is to detach winter leaves from _P. esseriana_,
I think that leaf dispersal by spring rain is a deliberate propagation
mechanism. Sometimes the entire plant fairly "shatters" apart when
trying to mail plants in winter growth.
-- Rick