I am experiencing a similar issue, but with xtype: 'menuitem'.
Preface: I am new to Architect, so this likely has something to do with this as well!
This is from creating a new extjs 4.2 project in Architect.
In architect 2.2.0 build 908, I add a tooltip by selecting the menu item in the inspector, clicking on the "edit" button next to the "tooltip" element in the config panel, and I then type in the tooltip text (I've tried with single quotes, double quotes and no quotes at all and the result is the same). When I look at the class in code view, I have an exclamation point next to the line number indicating that it has detected an "invalid value, config value converted to string". And in the config panel, the tooltip element is highlighted by a red bar on its left.
Not sure if this is related to the previous issue. If not, should I instead raise it a a separate bug?