I just moved back to the US from living overseas for several years. I've been trying out generic stuff, seeing which store brands were as good as the name brand, and most have been as good. I grabbed a generic cake mix, just to test it out. I used the extender recipe I found on one of the forums, and mixed it up. It was pretty thick going into the pan. I poured most into a 9x13, and the rest into a 5-heart cupcake type pan (i found it at a thrift store and wanted to try it out, which is why I did the extender recipe, to get a taller 9x13 and enough for the heart cakes.)
Anyway, the hearts came out fine, and I pulled them out around 20 minutes. I was baking at around 300, so I'd get even rising. (I've done that before, no problem.) I kept looking at my cake through the window, and it wasn't rising! The only time I opened the door was to get the hearts out, but I've never had problems before when I have different size cakes in the oven at the same time and have to pull some out sooner. The 9x13 was as flat as it was when I poured it in!
Luckily, I had a Duncan Hines mix that I forgot I bought, so I was able to use that for my husband's coworker's cake. The generic cake tasted alright, but it's a little dense. But I'll never buy generic again, just to save the 30 cents!!
Thanks for the warning. This is good to know.