Why does facebook always change privacy settings to custom?

[twenty one]

I set my privacy settings to 'friends only' but each time facebook decides to change it to custom without warning so my private info is exposed for all the world to see.

Why do they do this? And how does one know when they decide to change it?

[tmc]

i agree. i have to check my settings every day. i don't like it when i set my email to "me only" and it's like that for a while then suddenly it's set to where friends can view it!