I'm on a MacBook Pro with Yosemite, and I just downloaded and tried both the released 1.5 and the Nightly; I can't type or paste to the editor window. I can highlight the existing text, but no actual input interaction. Has anyone else seen this?
When I downloaded the source code and built it myself, it seems to work. If I see anything more specific, I'll report an issue.
You should double check that 'Use external editor' isn't checked in Arduino Preferences.
What you describe is exactly what would be the result.