OK. I don't know the root cause, but the resolution points to a bug in the all-classes.js ExtJS file.

Head over to the JSFiddle example referenced above.
Note the all-classes.js file soured in the 'Managed Resources' tab on the left.

If you have this file on your server, comment out the 2 very long lines starting with:

Ext.define("MyDesktop.BogusModule", .....
Ext.define("MyDesktop.BogusMenuModule", .....

Chances are you don't need them in your webtop/desktop app. If you do, start looking there.

THANK YOU all for helping!