Pretty printers don't work correctly for Qt4 built within namespace

There is a problem with displaying Qt classes when debugging program linked against Qt4 built within namespace. Perhaps, ditto for Qt5, but I didn't test.

To reproduce:

1. Build Qt4 in some namespace;
2. Create a simple program like: 

   int main()
   {
       QString tst = "foobar";
       return 0;
   }
   

1. Set break point on tst;
2. Start debugging.

Actual:

The string is displayed without pretty printers applied.

Expected:

Only "foobar" is displayed as a string value;

Regression:

Everything works as expected in QtCreator 4.0.