The issue which seems to be unique to Flurry SDK 4.2.2:
In 4.2.2 there is a new method:
+ (void)setBackgroundSessionEnabled:(BOOL)setBackgroundSessionEnabled;
It automatically gets set to YES
if there are any UIBackgroundModes
for your app. Our app uses the GPS in the background. Therefore Flurry will never post session data when going to the background.
When I force [Flurry setBackgroundSessionEnabled:NO];
then it sends up the session data when the Home Button is pressed and the app goes to the background.
I am not sure how this could ever work otherwise. We don't have a need to use Flurry to update GPS locations so this can work for us now.
Hopefully this helps others struggling with this problem.
Update: 6/17/2014:
I found more on this in Flurry's FAQ