merge says that a directory is not versioned, but it is

[Óscar Fuentes]

Output of `bzr merge':

Conflict adding files to tests/cases/thread.  Created directory.                                
Conflict because tests/cases/thread is not versioned, but has versioned
children.  Versioned directory.
Conflict adding file tests/cases/thread.  Moved existing file to
tests/cases/thread.moved.
Contents conflict in tests/cases/thread/thread-wrapper.wra

"tests/cases/thread" is versioned. In fact, the working copy is
pristine. That directory contains the same files on both branches, so
there is no file to add, just merge the changes to one of them. Is this
a bug or there is a cause for considering that the directory is not
versioned?

I also find complex to resolve this kind of conflict.