I'm having strong magenta cast. issues, too. They seem to date from my new LR4 installation.
Two printers - a 4800 and a 9800, both running identical inksets.
Three media, each profiled for both printers.
On two of the profiles on both printers I get a strong magenta cast on all media. Whether printing from LR or Qimage.
The third profile has no cast on both printers for all media.
All profiles re-installed - no change.
How weird is THAT?