--- a/mercurial/commands.py	Wed May 01 15:34:45 2013 -0500
+++ b/mercurial/commands.py	Tue Apr 30 21:12:49 2013 -0500
@@ -818,6 +818,14 @@
                 bmctx = repo[marks[mark]]
                 divs = [repo[b].node() for b in marks
                         if b.split('@', 1)[0] == mark.split('@', 1)[0]]
+
+                # allow resolving a single divergent bookmark even if moving
+                # the bookmark across branches when a revision is specified
+                # that contains a divergent bookmark
+                if bmctx.rev() not in anc and target in divs:
+                    bookmarks.deletedivergent(repo, [target], mark)
+                    return
+
                 deletefrom = [b for b in divs
                               if repo[b].rev() in anc or b == target]
                 bookmarks.deletedivergent(repo, deletefrom, mark)

--- a/tests/test-bookmarks.t	Wed May 01 15:34:45 2013 -0500
+++ b/tests/test-bookmarks.t	Tue Apr 30 21:12:49 2013 -0500
@@ -611,3 +611,19 @@
      Z@1                       1:925d80f479bb
      four                      3:9ba5f110a0b3
      should-end-on-two         2:db815d6d32e6
+
+test clearing only a single divergent bookmark across branches
+
+  $ hg book foo -r 1
+  $ hg book foo@1 -r 0
+  $ hg book foo@2 -r 2
+  $ hg book foo@3 -r 3
+  $ hg book foo -r foo@3
+  $ hg book
+     Z                         3:9ba5f110a0b3
+     Z@1                       1:925d80f479bb
+   * foo                       3:9ba5f110a0b3
+     foo@1                     0:f7b1eb17ad24
+     foo@2                     2:db815d6d32e6
+     four                      3:9ba5f110a0b3
+     should-end-on-two         2:db815d6d32e6