I've checked back via the GoDaddy interface, and all twelve domain names are still available (on all the TLDs that GoDaddy sells) at the original price.

This doesn't necessarily mean that GoDaddy doesn't ever take domains - maybe they only do it from high value customers who they think they can extract more money from, rather than people who aren't logged in; maybe I searched for too many domains with too few common substrings so their algorithm classified me as not wanting to seriously buy; maybe I didn't wait long enough because they manually decide which ones to buy; maybe the names I tried are too long to be considered valuable.