Must be a 64-32 bridge issue as I just run 12 tracks with an instance each and not even using buggy mode in Win XP 32.
Reaper's bridge should be as good as they come, but maybe try
jBridge as an experiment.
You could also try to go a step further than 'buggy mode' and run Radian as dedicated or separate process (you can find the options (Run as) by right-clicking the plugin name in the 'Add FX' dialog box (window).