Hey guys, Thought I'd sign up and share this one as it's a bit of a niche problem we found here in Australia.
Vodaphone Australia seems to pass its 3G data through a transparent proxy - which applies some kind of compression/transformations on the data going through it. This causes Sencha Touch apps to recieve a scrambled manifest file and stops the app from working.
To overcome this we have found that the following needs to be applied in CPanel on the server that the app resides.
Add the mime type: text/cache-manifest manifest
In Software/Services>Optimize Website apply 'Compress All Content'
Hope that comes in handy to any aussie Sencha devs