The way I solved that problem was by assigning a unique requestCode when you get the PendingIntent:
PendingIntent.getActivity(context, requestCode, showIntent, 0);
By doing so you are registering with the system different/unique intent instances.
Tip: A good way of making the requestCode unique would be by passing to it the current system time.
int requestID = (int) System.currentTimeMillis();