Just noticed this:
1. Open a sequence containing some clips.
2. Open the 'Sequence settings' dialog.
3. Change some settings in the 'General' pane.
4. Hit the 'Cancel' button.
Excepted result:
Changes made will be canceled, and not applied.
Actual result:
Changes are applied. The 'Cancel' button works as a 'ok' button, when changes are made in the 'General' pane. And you cannot undo either.