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?