Image analyzer settings are not loaded properly, due to reference removals while porting to PHP 5. One of the side effects is that image filtering might not work properly if matching on some specific analyzer info is used. An example of this is the default override for animated GIFS, which uses the is_animated info:

[AnimatedGIF]
# The MIME type which this override works on
MIMEType=image/gif
# A list of matches that needs to be satisified for this override to be used
Match[is_animated]=1