[Newbies] Anomaly of disappearing element in Bag?

Hello,

Item "disappears" in Bag after contents of the item changes. Item is container with equality and hash is overridden. Is this a Bug?

bag:= Bag with: (val := AKContainer value: 'a'). val value: 'b'. bag valuesAndCounts includesKey: val. "false in Trunk,"

set:= Set with: (val := AKContainer value: 'a'). val value: 'b'. set includes: val. "true"

dictionary:= Dictionary newFromPairs: {val := AKContainer value: 'a'. 1}. val value: 'b'. dictionary includesKey: val. "true"

All tests fails in Squeak 3.6 and in Dolphin ST. In Trunk fails only the Bag.

If this is not a bug, how can I escape this Anomaly of disappearing element [1] Thank you Vaidotas

[1] http://books.google.lt/books?id=W8_Une9cbbgC&pg=PA76&lpg=PA76&dq...