missing main.cpp

When i delete for mistake "main.cpp" file from my project i cannot add it again, but the code from this file still run normaly. For example: When i create new plain c++ aplication project, and next i delete "main.cpp" from my project: theres no way to add this file again.

To let you know what is the problem try to:
1. Create new Plain C++ Aplication.

2. Delete "main.cpp" file.

3. Try to add it again to the same project - (Qt Creator don't add it back)

4. Try to run this aplication - (it gonna compile and run)