Copy and paste not working in Edit CSS page

Copy/Cut and paste in the Edit CSS page is not working properly, but is working in the Editor page.

I’ve tried using Edit CSS in the current release of both Safari and Firefox, with the same results: I can cut text, but I can’t paste it. I can’t copy text – Pasting the copy inside the Edit CSS page (and outside in a text editor application) fails silently. I’ve tried both keyboard shortcuts and menu pull-downs, with the same result. The problem has persisted across sessions, with full shutdown and startups in between.

I’m on the current release of OSX on a MacBook Pro, and I’m stumped.