Since this feature is just broken and easy to work around I think it should be turned off. When I say broken I mean that you can't put apostrophe in chat at all. Every message with " ' " gets filtered off. I always try to write properly and find myself typing same thing twice or trice because I didn't remember to omit apostrophe sign.
This is something that absolutely all mu clients have inside but as you say it does have a work around by editing the filter.bmd file, however our sql injection regarding forbidden symbols is added on server side as well. Symbols like " ' , " == " and others are used for sql database injection and I'm sure none of us want such surprises. By default in all mu clients when you type the apostrophe sign you get that Pwned by the filter text but as I have said that protection is also added on server side as it can be bypassed on client side.