One more minor matter:
If you disable a condition by blanking all of its boxes, upon clearing the first field (the column field) the following exception occurs:
Code:
calibre, version 0.8.4
ERROR: Unhandled exception: <b>KeyError</b>:u''
Traceback (most recent call last):
File "/Users/griker/Documents/calibredev/source/dev/src/calibre/gui2/preferences/coloring.py", line 162, in init_action_box
m = self.fm[col]
File "/Users/griker/Documents/calibredev/source/dev/src/calibre/library/field_metadata.py", line 379, in __getitem__
return self._tb_cats[key]
KeyError: u''
G