Welcome to the ridiculous world of airline fares!! You are absolutely correct about the frustrating nature of the situation. Airlines often institute a fare sale with a ticketing deadline. Sometimes they keep the deadline, sometimes they extend it - and no one knows (probably even the airline officials themselves) whether it will be extended or not until the last minute. Sometimes, if a sale is scheduled to end on Friday, the fares go up on Saturday and Sunday, and then the sale is reinstituted on Monday.

If one could predict the whimsical nature of this situation, one could make a fortune in airline "futures". I wish I had a good suggestion. The only thing I can say is that if you buy a ticket and then the fare goes down, most of the time the airline will give you a voucher for the difference that you can use on a future flight.