a couple thoughts on this one , when you saved the pose to library, did you include morphs?.... after creating the custom morph, did you update the figure file to have the new custom morph in the figure the next time you loaded it?.... if you missed either of these steps its not going to work... dont feel bad if you made these mistakes , we all do it from time to time ,  best insurance against 'boo-boo's' is saving the scene so you can backtrack and fix things you may overlook...

EDIT:sorry i mis-read and thought it was a conforming figure, ill leave previous  post intact for those who may find it usefull, again you have to save the morphs to the pose and update the prop in library to include the new morph, also dont depend on the custom morph to stay intact during save and reload.... under the object tab click spawn morph target  name it something meaningful and delete/or zero the custom morph, again saving the PZ3 is always good insurance untill prop has been tested...

 

JAFO

Y'all have a great day.