I think I have found a driver bug with glPolygonOffset, in fact it is impossible to use it.
When I enable polygon offset via
// or: glPolygonOffset(0,1);
// or: glPolygonOffset(0.75f,0);
//do some rendering ...
The device shows the first rendered frame, then sudenly the menu, from where the app was opened, shows, and this repeats very fast. Also, now it is impossible to close the application and the screen keeps showing previous frames when the application is minimized. Everything works fine when disabling polygon offset via glDisable or glPolygonOffset(0,0).
My device is a Sony Ericsson Satio.