denis, that is interesting. Perhaps the CRAPPS system sees the standby flight as a one-way ticket made on short notice, just like all the terrorists routinely make.
If others have experienced this, the smart thing may be to retain your original BP (make a copy if you do online checkin) and use it to pass through the checkpoint instead of using whatever standby BP they issue you.
The other smart thing to do would be to wait until you're inside security before attempting to make changes to your itinerary, possibly at the club, assuming you have the time to do so.
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"Give me Liberty or give me Death." - Patrick Henry