I had that problem the other day, with the same cake and the same creamer. I used the liquid creamer. I don't know what the dynamics are but you are not alone in this problem, many other cake-a-tiers have had this issue.
I made it half recipe last week with not problem - expect my husband could tell it was from a box! He's so spoiled.
I made it yesterday -- half a recipe, substituted half white chocolate raspberry creamer and half milk, used three whole eggs instead of 4 egg whites. I made six cupcakes and split (or so I thought) the remaining batter in two 8" pans. I had one pan the worked fine and the other fell a little in the middle. I'm wondering if I had a little too much batter in the one pan (it was a little higher on the outside than the other pan)? Any thoughts?? 
Thanks for all your feedback. I am sure I added all the ingredients as I checked my recipe twice. I was thinking maybe my oven temperature is off. I have a oven themometor and I do go by that. I have been having some problems with other cakes falling also so maybe it isn't the recipe. I am frustrated though.
I seem to have this problem too. I usually sub butter for the oil and put half whole milk and water. The cakes alway seems to sink in the middle for some reason. I have a convection oven, so I dont know if that would have anything to do with it. If anybody figures it out let me know, too!
The liquid creamers are loaded with sugar and fat.
Too much sugar, fat or leavening in a cake recipe will cause the batter to not rise or the baked cake to fall upon cooling:
http://www.realbakingwithrose.com/2005/12/sugar.html
(See general uses of sugar.)
http://www.bakingandbakingscience.com/Cakes.htm
HTH
I just tried this tonight, the WASC cake with half white rsapberry creamer added in place of half the water, and it fell! I even baked it longer than I normally do.
I have baked the WASC cake hundreds of times with no problems, and from now on I will stick to the recipe, no subsituting the creamers. I will instead use the creamers in my buttercreme frosting.
You might try adding raspberry flavoring to just the cake recipe and put the creamer in the frosing. I tasted the cake and it seemed awfully sweet with the creamer added. I have made the WASC cake before without the creamer and it didn't fall. I think the creamer is the problem.
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