I have my registry editor set to Resplendent Registrar. I'm in the Registry Cleaner results window. If I right-click an item and select Open in RegEdit I get Registrar, but if I select an item and hit Ctrl+R I get Regedit.
As an additional wrinkle, if I select an item, right-click to get Registrar, close it, and hit Ctrl+R on the same item, I get Registrar. But if I move to a new item and hit Ctrl+R on it, I get Regedit again.
Windows XP SP2, jv16 version 1.5.2.337