After upgrading to the current nightly build, the "Visual" tab on the editing screen for posts and pages has become disabled. The tab is visible but clicking it does nothing. It no longer switches into visual editing mode. Only the "Upload/insert" line of editor icons remains visible above the edit window. The rest of the visual editor icons are missing. I checked my profile and I do NOT have the "disable visual editor when writing" box checked. (Checking that box makes the "Visual" tab go away.) I tried disabling two plugins that affect the editor (footnotes and search-and-replace) but that had no effect. Could this be a bug?