Keywords view: Deleting inherited values does not work

When you have set a keyword set in a cossreferenced parent item, it is
inherited to the child items.
Removing the keywords from the childs in the "keyword view" does not
work:
Pressing the delete key when one or more childs are selected should
remove the keyword, but it generates an error message:

*** -[NSPlaceholderString initWithCapacity:]: selector not recognized [self
= 0x425b30]

Removing the keyword manually works as expected.

(I am not sure if inheriting the keywords to the childs does make sense at
all, maybe this should not be done or there should be an option!)