Bug in assoc:map_assoc/3

[edechter]

The following should succeed but doesn't:

bash-3.2$ yap
YAP 6.3.4 (x86_64-darwin13.4.0): Wed Feb 10 11:32:28 EST 2016
 ?- use_module(library(assoc)).
 % reconsulting library(assoc)...
  % reconsulting library(rbtrees)...
  % reconsulted /usr/local/Cellar/yap/6.3/share/Yap/rbtrees.yap in module rbtrees, 11 msec 0 bytes
 % reconsulted /usr/local/Cellar/yap/6.3/share/Yap/assoc.yap in module assoc, 13 msec 0 bytes
true.
 ?- list_to_assoc([a-1], A), map_assoc(succ, A, B).
false.
 ?-