qmake processes my pro file several times

I have a pro-file:

Code:

message("This message should be appeared only once!!!")
CONFIG += qt release
SOURCES += src/main.cpp

I call qmake:

Code:

set QMAKESPEC=win32-msvc2008
set QTDIR=c:\Qt\4.8.4_vs2008\
 
call "C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\vcvarsall.bat" x86
call "%QTDIR%\bin\qmake.exe" -tp vc Server.pro

... and I got a very strange output:

Code:

Setting environment for using Microsoft Visual Studio 2008 x86 tools.
Project MESSAGE: This message should be appeared only once!!!
Project MESSAGE: This message should be appeared only once!!!
Project MESSAGE: This message should be appeared only once!!!

The question is: why did it process pro file THREE times instead of one?