Leaving intentional bugs in code for testers to find

We don't do this at our firm, but one of my friends says that his project manager asked every dev to add intentional bugs just before the product goes to QA. This is how it works:

1. Just before the product goes to QA, the dev team adds some intentional bugs at random places in the code. They properly back up the original, working code to make sure that those bugs aren't shipped with the end product.


2. Testers are also informed about this. So they will test hard, because they know there are bugs present and that not finding them might be considered as a sign of incompetence.


3. If a bug (intentional or otherwise) has been found, they will be reported for the dev team to fix. The dev team then adds another intentional bug in a related section of the code just before product goes to 2nd level QA. The project manager says a tester should think like a developer and he/she should expect new bugs in sections where changes were made.

Well, this is how it goes. They say that this approach has following advantages

1. Testers will be always on their toes and they will test like crazy. That helps them to also find hidden (unintentional) bugs so developers can fix them.


2. Testers feed on bugs. Not finding any bugs will affect their morale. So giving them an easy one to find will help their morale.

If you ignore the scenario were one of these intentional bugs gets shipped with the final product, what are the other drawbacks we should consider before even thinking of adopting this approach?

EDIT :

It has been 2 days and there are lot of answers. But I want to make something clear.

1) They properly backup the original code (Yes, they use source control, backup was a general term)

2) When tester find out an intentional bug, dev team just ignore. If tester finds out a unintentional (original) bug, dev team first check whether it is caused by any of the intentional bug. That is, dev team first try to reproduce that on original working code, and fix it if they can.

3) Just ignore the relationship issues between QA - Dev team. I specifically asked this question on programmers not on workplace. Consider that there is good rapport between QA and Dev team and they party together after working hours. Project manager is a nice, old gentleman who is always ready to support both teams(Godsend).