In my application on the Nokia 3650 the softkey button text ( Cba buttons ) is not updated in time when the menu button text is changed after a menu change or opening of a menu pane. It can take up to 5 seconds before the text gets updated. I tried DrawNow() and DrawDeferred() on iEikonEnv->AppUiFactory( )->Cba( ) but no success. I also tried to flush the window server... also no success. Updating remains totally unpredictable.
In my app I've got a periodic timer called every 15 milli seconds and a second thread working at high priority, but I think there should be enough cpu time left to update the button text.
I think you should do some experiments with increasing the time for your timer or decreasing the priority for your tread, at least for me it sound that your system doesn't have enough time to do the re-drawing, since the drawing is working on lower priority than your busy working tread.