Spawn Protection for custom Servers not working

Hi! I downloaded the 1.5 Prerelease Server EXE and Minecraft and tried a custom made world and a few newly generated worlds but it seems Spawn Protectoin does not work. I tried it in Adventure and Survivale gamemodes with Spawn Protection set to 6 but I can destroy blocks anywhere at the spawn area and hit torches, glass or grass in Adventure mode in the spawn area (may be intended). I have no OP rights and was not in creative mode.