If I'm using rdebug-ide to debug a process, like rails, that takes it upon itself to require 'ruby-debug', then things fail because both ruby-debug and ruby-debug-ide end up defining Debugger:RemoteInterface with a different superclass. Not sure how you want to deal with this, maybe different namespacing of classes between the gems?
I hacked a workaround by monkey patching require to not skip loading ruby-debug if being run from rdebug-ide. See here for more details:
http://youtrack.jetbrains.net/issue/RUBY-5782#comment=27-145268
p.s. is this the right place for issues?