Qt 4.7.1 DirectFB surface not released?

I intergrate QT4.7.1 with DirectFB 1.4.1 Phase 2.5, but after browsering several pages with the QT demobrowser,the following error occured.I add printf statement when requests createSurface operation and releaseSurface,and found some surfaces create are not released?

Code:

(!) bcmNexus/Pool: NEXUS_Surface_Create failed!
(!) bcmNexus/Pool: NEXUS_Surface_Create failed!
(!) Core/SurfBuffer: Buffer allocation failed!
    --> General failure!
(!) bcmNexus/Pool: NEXUS_Surface_Create failed!
(!) bcmNexus/Pool: NEXUS_Surface_Create failed!
(!) Core/SurfBuffer: Buffer allocation failed!
    --> General failure!

My bootscript file

Code:

#!/bin/sh
mount -t nfs -o intr,nolock,rsize=1024,wsize=1024 10.0.3.134:/opt /home
mount -t nfs -o intr,nolock,rsize=1024,wsize=1024 10.0.3.134:/home/dfb /usr/local
export export gfx_heap_size=20000000(The bigger size setting,the later error occur)
export QWS_SIZE=1280x720
export QT_INSTALL_DIR=/home/qt471
export QT_QWS_FONTDIR=${QT_INSTALL_DIR}/lib/fonts
export QT_PLUGIN_PATH=${QT_INSTALL_DIR}/plugins
export LD_LIBRARY_PATH=/home/qt471/lib:$LD_LIBRARY_PATH
export LD_LIBRARY_PATH=/home/qt471/extralib:$LD_LIBRARY_PATH
export LD_LIBRARY_PATH=/usr/local/lib:$LD_LIBRARY_PATH
cd /usr/local/bin/directfb/1.4
./rundfb.sh ${QT_INSTALL_DIR}/demos/browser/browser -qws -display directfb -font simhei http://10.0.3.37/index.asp

qmake.conf

Code:

#
# qmake configuration for building with mipsel-linux-g++
#
 
include(../../common/g++.conf)
include(../../common/linux.conf)
include(../../common/qws.conf)
 
# modifications to g++.conf
QMAKE_CC                = mipsel-linux-gcc
QMAKE_CXX               = mipsel-linux-g++
QMAKE_CFLAGS           += -mips32
QMAKE_CXXFLAGS         += -mips32
QMAKE_LINK              = mipsel-linux-g++
QMAKE_LINK_SHLIB        = mipsel-linux-g++
 
# modifications to linux.conf
QMAKE_AR                = mipsel-linux-ar cqs
QMAKE_OBJCOPY           = mipsel-linux-objcopy
QMAKE_STRIP             = mipsel-linux-strip
 
QT_CFLAGS_DIRECTFB = -I/home/dfb/include/directfb -D_REENTRANT
QT_LIBS_DIRECTFB = -L/home/dfb/lib -ldirect -ldirectfb -lfusion -lz 
load(qt_config)

Thank you for your tips.