The release of QuickTime 7.5 appears to have fixed the problems that 7.4.5 introduced, with regard to LiveType elements not rendering and green screen keying software not working with the K3 enabled for output. It not only cured our existing setup, but a complete erase and reinstall of all software verified that it is indeed gone.
I'd like to thank:
1) The users here, on the FCP forum and the LiveType forum who verified my reports and diligently reported this to Apple. This is a great example of how useful the COW can be.
2) Apple for contacting me after my detailed feedback report... and for taking this seriously.
3) Rudy and the team at AJA for getting involved and testing on their end.
4) The folks at Red Giant for getting involved and through testing, discovered that it affected many keyers, including Apple's own.
We're back in business and can now use Primatte again, one of the best chroma-keyers we've ever used...