Sorry to resurrect this zombie thread, but I think I've found the solution to my problem. Usually I hydrate binder and filler on Friday, roll and press dolls Saturday, hydrate wrapper Saturday and wrap Sunday. For reasons beyond my control, on a recent rolling weekend I was unable to wrap Sunday and left the hydrated wrapper leaves in the bag an extra day. Much more pliable and easier to work with overall. Here's my thinking:
The stem and veins are the moisture transport mechanisms of the leaves. When I spray the leaves a substantial portion of the water migrates to the transport system and equalizes the moisture content throughout the leqaf. By giving that process an extra day before destemming, my leaf had a more uniform moisture, and was able to migrate further towards the leaf edges.