Shared toolbar doesn't reflect state of the editor

[Alfonso Martínez de Lizarrondo]

1. Load Sample 10
2. Focus First editor, then go to second editor
3. Switch to source mode. The toolbar changes to source mode
4. Focus the first editor. The toolbar changes to design mode
5. Focus the second editor.

Now the toolbar remains in design mode. (once I've seen all the buttons disabled in Firefox, and also directly in step 3 the toolbar remained in design mode)

Now the buttons are available but they give an error (#670)

[Alfonso Martínez de Lizarrondo]

dup of #772