This happened TWICE today and I am extremely frustrated. Before I bake AGAIN any help is appreciated.
12 inch square Magic Line Pan
Used 2 Aldi's white cake mixes straight up. Nothing doctored.
Baked at 350 degrees.
Cake came out looking fine.
1st time I left it in the pan for 10 min to cool and when I checked it had completely shriveled in all directions.
2nd time I tried leveling in the pan and them immediately turning on cooling rack. Same problem.
Let me add that today I baked 8 other cakes using the exact same mix but various size pans and did not have any problems. I even baked another 12" square and it turned out fine.
Any ideas on why my cake just completely shrunk up?!? 
Here are two links which give several reasons for cakes shrinking:
http://www.bettycrocker.com/products/supermoist-cakes/faq
http://tinyurl.com/yay22w
HTH
I am beating on low for 1 minute to combine everything. scraping down the bowl and then beating on med-high for 3 minutes.
using home-made cake release in the pan
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