How come bzr says there is nothing to do on merging branches that differ one from another?

I have a bizarre situation with two bzr branches. The two branches differ one from another as can be seen here:

$bzr diff --old=/path/to/another/branch | wc -l
148

However, when I'm trying to merge these two branches, bzr says that there is nothing to do:

$bzr merge --preview /path/to/another/branch
Nothing to do

I tried to touch the files in the another branch in order to modify their modif开发者_开发技巧ication times, but this didn't help. What am I missing here?

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well, it turns out that I had to do bzr status in the target branch. Doing this I discovered that

working tree is out of date, run 'bzr update'

This actually solved the problem. After updating, the both branches became identical, as expected.