Anything that fails in CFRunLoop is a known issue. Essentially I wrote the tests, but Ivan to run them and haven't had time to work on corebase for many months now. CFRunLoop isn't there except for stubs. It's one of those that I'll get to one day when I have more time.
Also, keep in mind that despite being able to do some basic toll-free bridging and interaction with base, corebase is still not well integrated with the rest of GNUstep. I'd be interested to know if you actually build any software against it and what bugs you run into.
Stef