I have encountered similar (nearly unexplainable) behavior
Found a reference to deleting .exd files under the directory C:\Users\username\AppData\Local\Temp Located one in each of the directory Excel8.0 and VBE. Typical name is MSForms.exd
Google "Excel exd" or "KB 2553154" From my perspective, it is a completely unacceptable situation which has been there for at least a month now.