Hi Paul,
If you typed in "DESC [tablename]" and pressed F5 in the editor and received this incorrect result, this issue was recently identified and was actually just fixed. It should be in the beta that will be released today. If you get a chance, make sure you have Toad 13.1 installed and download the Toad for Oracle beta from here this afternoon:
That should fix the issue you're seeing. Please feel free to let us know if this does not solve the issue you're seeing and we'll continue to look further.
Thanks!
-John