oh well, hopefully filter will be improved in a later version and the inconsistent behaviour removed, I see no reason why it shouldn't work in the types of windows I've mentioned.
Dcc chat windows are also handled inconsistently with window identifiers, if I have a chat window open to the nick frazzle, $active is =frazzle, but $line($active, 0) returns null, I have to use $line(Chat frazzle, 0) to get a correct value.
Locutus... I know normal custom windows can't have spaces in them, but you have little choice when dealing with mirc's own windows.