If you try to update from 3.1.0-b1 to 3.1.0-b2 you get an error:
The update files are incomplete.
FILE: (not given by php)
LINE: (not given by php)
This is due to deleted files being named in the diff as all content replace with nothing.
The script extracting the file names does not check for this case.
However, it is strang that this is reproducable on b1>b2, but not on 3.0.12>b2 although the same file is listed incorrectly in both packages