I tested in 5.28pre5, and it works for me as well. I really appreciate your help.
Would you be able to take a look at the other issue I reported at the same time as well?
http://forum.cockos.com/showthread.php?t=182297
That issue may be more of a feature request than bug report, and you may want to make some design considerations of your own with respect to whether (and how) to address it. But for cyclic parameters (like the azimuth angle) folding interpolation will be useful.