Strange failure (dialog exec close qt 5.1)

[giancarlo.fir]

the simple attached program works properly on x86 desktop and works bad in arm embedded system.
The program has a button in the main window if i press the button the dialog exec function is called.
On the dialog I can press an button to close it.
On x86 platform run correctly, on arm when I close the dialog it does' t disappear and can't capture the input.
why this difference?
I use
gcc version 4.6.2 20110630 (prerelease) (Freescale MAD -- Linaro 2011.07 -- Built at 2011/08/10 09:20)
and I start the program with this script
export QT_QPA_EGLFS_HIDECURSOR=1
export QT_QPA_EGLFS_PHYSICAL_WIDTH=150
export QT_QPA_EGLFS_PHYSICAL_HEIGHT=95
export LD_LIBRARY_PATH=$LIBRARY_PATH:/opt/Qt5-imx6-1/lib
./focus -platform eglfs
Thank you