facebook dialog failing silently when not called immediately after authorize - iphone

Question

I have the following function to post to Facebook using the latest iOS Facebook SDK.
-(void)fbPost:(NSMutableDictionary *) params{
NSLog(#"fbPost called");
if (![facebook isSessionValid]) {
NSLog(#"session invalid, calling fblogin");
[self fblogin];
}
if ([facebook isSessionValid]) {
NSLog(#"session valid, calling publishToFB");
[self.facebook dialog:#"stream.publish" andParams:params andDelegate:self];
}
}
It works fine when there is no existing session: it logs in to facebook, gets permissions, returns to the app, shows the dialog and publishes the status. However, when trying a second time, isSessionValid returns true the first time and nothing happens, although the log shows publishToFB is called.
The session is persisted in fbDidLogin:
[[NSUserDefaults standardUserDefaults] setObject:self.facebook.accessToken forKey:#"AccessToken"];
[[NSUserDefaults standardUserDefaults] setObject:self.facebook.expirationDate forKey:#"ExpirationDate"];
[[NSUserDefaults standardUserDefaults] synchronize];
and loaded in application didFinishLaunchingWithOptions:
facebook.accessToken = [[NSUserDefaults standardUserDefaults] stringForKey:#"AccessToken"];
facebook.expirationDate = (NSDate *) [[NSUserDefaults standardUserDefaults] objectForKey:#"ExpirationDate"];
I made sure to ask for offline_access permission when logging in:
_permissions = [[NSArray arrayWithObjects:
#"publish_stream",#"offline_access",nil] retain];

Answer 1

It appears the problem was in drawing the dialog in this code in FBDialog.m
UIWindow* window = [UIApplication sharedApplication].keyWindow;
if (!window) {
window = [[UIApplication sharedApplication].windows objectAtIndex:0];
}
If I comment out the If clause, it works OK. I guess that in my app setup, "keyWindow" is not front-most, so the dialog was not showing up.