To reproduce:
In Pages app, open a page with a text/image component (/demo-project/about/subsection-articles/an-interesting-article:tree in the page editor.
Edit a text/image component (for example "More interesting").
Click "Save Changes".
> Page reloads.
Edit the same text/image component.
> Nothing appears to happen.
Close the Editor SubApp.
Now you see the text/image dialog in a corrupted state. Only a text tab, no actions.
There is no way to close the dialog and the UI is blocked.

Its a very similar pattern to: http://jira.magnolia-cms.com/browse/MGNLUI-362
And therefore seems likely that it is a general problem with dialogs.

Additional Notes:
The problem happens on the second opening regardless if you have closed the subapp editor, or even the entire pages app. Only a "?restartApplication" resets the issue so that you can open the editor again. (This is the same with the Showcase dialog problem. - closing app does not help.)

Cannot make the problem happen on other dialogs:

• Page Editor: Edit page properties
• Security App: Edit user, Edit group