Starting to use labels and at first all seemed okay, but now I have noticed 2 things that are causing problems:
  1)  I created a smart playlist that used a rule of  "label contains xyz".  For a couple of label values this rule generates no songs, even though there are definitely a few songs with this label.  Going back and checking the songs confirms that they do indeed have that label.  For other labels it only generates a partial listing even though other songs have those labels.  Cannot find any trend that might indicate a problem.  I have songs with 1 to 4 labels showing up, and songs with 1-4 labels not showing up. 
  2)  I noticed that in the track properties dialog for labels that it says "favorite labels".  Also noticed that not all of the labels I have defined are listed there.  Not sure if this is by design or is trully a bug.  But in my mind the place where you set labels should show you all of your labels.  I have some obscure ones that are not used all the time and forget whether I named it xyx or zyx, so then I have to go to another screen where and confirm what the right value should be.  Should just present all of them on this dialog.

Looking at the database directly yielded no direct clues as the labels are in some special format.  Did not have time at the moment to check the code.