Undo a wrong merge with Bazaar

[TRIDENT JOB]

Hi BZR community !
I have an issue while using Bazaar and I would like to get the best practices to fix it. Here is the context:In the trunk of our project, one wrongly merged a branch (BranchA) in the trunk but he used revert on most files while keeping the merge info (so from bazaar BranchA was effectively merged in trunk, preventing to REALLY merge it later).
The merged revision was committed as r4.After this (undesired) merge, many devs committed right after (r5 & r6).So my question is : how to undo this wrong merge ? (while keeping the commits after).I tried to uncommit back to r3 and merge each rev from r4 to R6 (omitting r4)
I tried 'reverse cherry pick' r4 ... but the BranchA merge information may still memorized.trunk
  |
  r6
  |
  r5
  |    branchA
  |     |
  r4 ---+
  |     |
  |    r2.2
  |     |
  r3   r2.1
  |     |
  r2 ---+
  |
  r1
If you have a solution or some clue to fix it, please share it !
(for example can REBASE command help here?)
---

The source thread on SO:http://stackoverflow.com/questions/24246606/undo-a-wrong-merge-with-bazaar
thx for you help.
 		 	   		  
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