Occasionally players will not be able to use nether portals ( they just stand in them and it does nothing) this is fixed if they destroy and replace their city protection but the cause seems to be random , please let me know if this is a known issue that i have caused or if its a bug.

Let me know if you need any more info.

Remove or disable the "prevent-portal-enter" flag from the field if it contains it. http://preciousstones.shoutwiki.com/wiki/Field_Flag_Reference#prevent-portal-enter