Minecraft Spawn Protection does not work

Spawn protection is off if there are no OPs.

Where is this documented? Its not on the wiki.

https://twitter.com/Dinnerbone/status/253986918897942528

Doesn't makes sense to me, why it deactivates in case no OPs (for me its to protect the spawn from beeing changed from non-OP users, independet if there are OPs or not) are set, but thanks for clarification.

If there are no OPs, it assumes you're on a vanilla survival server with a controlled amount of people (I.E. your friends, because there's no one there to ban people) and therefore intend to populate the spawn area. If there are OPs, it assumes that your server is going to be under moderation and allowing people you don't know into the server, so it stops people from griefing the spawn area so that new players don't fall into pits of lava that some random idiot put down.
I recommend adding something random to the ops.txt list that gets counted as a name, but isn't.

Thanks for the explanation, but i tried to activate a fake OP (its the first time we have no one who really gets to be OP, i "restricted" myself to normal rights), but its already to late. I Build a house that is with big shares on the spawn area, so its too late for this server...

You can make the spawn area smaller in server.properties or set the world spawn with:
/setworldspawn <x> <y> <z>
or if your are standing on the right place you can use:
/setworldspawn