In FB 10.4.15 when one of the precip type grids (WxIP, WxR, WxS,
WxZR, etc) is actively selected, and the Copy PoP to Selection
button(in the Precip Types Step) is clicked (attempting to copy the
current PoP grid into that corresponding p-type grid), the selected
grid is deleted.
This appears to be a bug.
-Brian