Well.. if you had poked around in WrpEditor on that island you could have changed something.. but that's the only way I can think of.. and then it wouldn't really only happen on that mission .. but any on the island...
My only suggestions if you haven't tried them are:
Select everything in your mission then copy+paste it into a fresh version of the map
Save the mission folder and reinstall OFP
In the end I'm going to have to say consult the official forums @
www.flashpoint1985.com because it would seem to me to be a bug of some sort and not really mission editing related....
they have troubleshooting forums over there and people who might be more familiar with the problem you're having
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