qt 4.7.4 linking error, missing --enable-auto-import

[lvdong]

I compiled qwt 6.0.1 dynamic library with qt 4.7.4, and added it to my qt project,
but there is a linking warning saying missing --enable-auto-import option,
I checked the qmake.conf file in mkspecs/win32-g++, QMAKE_LFLAGS is empty,
QMAKE_LFLAGS =
but in qt 4.7.3, QMAKE_LFLAGS = -enable-stdcall-fixup -Wl,-enable-auto-import -Wl,-enable-runtime-pseudo-reloc
so I added the -Wl,-enable-auto-import to qt 4.7.4, it worked.
I am confused.

env: win7 32bit, qt 4.7.4, qtcreator 2.3.0
log:

g++ -mthreads -Wl,-subsystem,windows -o debug\mpbs.exe object_script.mpbs.Debug -L"c:\Qt\4.7.4\lib" -lmingw32 -lqtmaind debug\mpbs_res.o -Ld:/qwt-6.0.1/lib -lqwtd -lQAxContainerd -lole32 -loleaut32 -luser32 -lgdi32 -ladvapi32 -luuid -lQtGuid4 -lQtCored4

Info: resolving QwtPlot::staticMetaObject by linking to __imp___ZN7QwtPlot16staticMetaObjectE (auto-import)

c:/qt/qtcreator-2.3.0/mingw/bin/../lib/gcc/mingw32/4.4.0/../../../../mingw32/bin/ld.exe: warning: auto-importing has been activated without --enable-auto-import specified on the command line.
This should work unless it involves constant data structures referencing symbols from auto-imported DLLs.