Possible bug in XSyncValueSubtract

I think there might be a bug in the XSyncValueSubtract macro in the SYNC 
extension. The following test program demonstrates it: 
 
----- start test program ------ 
 
#include <X11/Xlib.h> 
#include <X11/extensions/sync.h> 
#include <stdlib.h> 
#include <stdio.h> 
#include <unistd.h> 
 
int main() 
{ 
    XSyncValue one, two, res; 
    Bool overflow; 
 
    XSyncIntToValue(&one, 1); 
    XSyncIntToValue(&two, 2); 
 
    XSyncValueSubtract(&res, two, one, &overflow); 
    printf("result=%d:%d\n", res.hi, res.lo); 
    printf("overflow=%d\n", overflow); 
    return 0; 
} 
 
----- end test program ----- 
 
The output of this program should be:  
result=0:1 
overflow=0 
 
Instead, the output I get is: 
result=-1:1 
overflow=1 
 
This bug breaks the semantics of XSyncAwait, causing it to not send 
XSyncCounterNotify events when a trigger is fired and the client is unblocked. 
The bug appears to be present in both the XFree86 code and the KDrive code. 
 
Sincerely, 
    Rayiner Hashem