SVV mergeinfo property and branches

Here we go again to svn: mergeinfo. I've read all the Q / A's regarding this, but I ran into a situation that doesn't seem to be addressed in the existing posts here. My chest is clean from svn: mergeinfo i.e. It:

svn propget svn:mergeinfo --depth=infinity

      

        
        
        
      

    

only returns information about the merge into the root string, which is good. I create a branch and that branch is fine too, with svn: mergeinfo only at the root of the branch. But then I try to update the branch with the last line, like:

svn merge http://xxxxx/trunk

      

        
        
        
      

    

And then a bunch of files (about 60) get the svn: mergeinfo property. Note that I had this problem before when 60 files had a mergeinfo property set to trunk and I removed it from the trunk and then detached it from the trunk. This way the properties are not on the trunk, not on the branch, they magically appear when I update the branch with the trunk.

Any ideas?