I use Dreamweaver for editing Ruby on Rails files, Velocity files, and other files that don’t have native support but that do have extensions available in order to use with DW.
Although after installing said extensions these file types open fine, have proper code coloring, etc., I’ve had the problem that they don’t open in Design view, which was a real pain!
As a workaround I found that if I did a Spell Check on these pages, Design view would open as a split screen and as long as I didn’t close the file or click the Code view button I was OK. But recently I found the real problem and a real solution!
It turns out that I was adding these file extensions to the Edit > Preferences… > File Types / Editors > Open in code view list prior to installing the Dreamweaver extensions for that file type. Which was obviously…well…opening them in the code view.