CGEventPost - possible bug when simulating keyboard events?

Question

I have a very simple chunk of code that is designed to simulate keyboard events. The simple example below should type \"Cz\" - the shift key goes down, the c key goes down,

Answer 1

Like another comment referring to other solutions here, after using uppercase with the Shift mask, a successive call would cause any further intended non-shifted character to be turned into an shifted characters. I figured the call to CGEventCreateKeyboardEvent was somehow saving previous masks, so I purposefully clear the mask of the modifier:

CGEventRef event1, event2;

CGEventSourceRef source = CGEventSourceCreate (kCGEventSourceStateCombinedSessionState);
CGEventFlags flags;

event1 = CGEventCreateKeyboardEvent (source, keyCode, true);
if (upper)
    flags = kCGEventFlagMaskShift | CGEventGetFlags(event1);
else
    flags = ~kCGEventFlagMaskShift & CGEventGetFlags(event1);

CGEventSetFlags(event1, flags);
CGEventPost(kCGHIDEventTap,event1);

event2 = CGEventCreateKeyboardEvent (source, keyCode, false);
if (upper)
    flags = kCGEventFlagMaskShift | CGEventGetFlags(event2);
else
    flags = ~kCGEventFlagMaskShift & CGEventGetFlags(event2);
CGEventSetFlags(event2, flags);
CGEventPost(kCGHIDEventTap,event2);
CFRelease(event1);
CFRelease(event2);
CFRelease(source);