I have found that the new Sencha 2.1 update is incompatible with Cordova 2.0. Can't give much more info: The same app with Sencha 2.0 works with the Cordova library while, if update to 2.1, it stops working (white screen after launch image). So the situation is the following:

Sencha 2.0 + Cordova 2.0 works but ios6 bug
Sencha 2.1 + Cordova 2.0 ios6 bug fixed but doesn't work