Cao may be right, have your bees swarmed and so you don't need the space.
Something doesn't add up, just because they have waxed frame 13, if it is not full of honey then why add more frame area.
Another 7 frames is a lot, when I would think the advantage of a long hive would be to just add a frame at a time as they fill the last one.
I am no expert on long hives.
Bees always run better when there is not extra space to look after.