the GONME and the command line in ubuntu,why different?

[supercodeing35271 supercodeing35271 <supercodeing35271 gmail com>]

As we know that there are various syscalls in linux kernel,the
sys_mkdir(),sys_open(),sys_fchmodat(),sys_fchownat ().Then,we can
intercept it .
Today i do a work about it,catch the chown syscall.
The file is "myfile",the owner is "my".We can use the command "chown
root myfile",then,"myfile"'s owner will change to root.After i used
strace for a look,i found the syscall in this situation is
sys_fchownat.I catch it,every time i use the chown command to change
the owner of "myfile",then a printk will into log.
But,when i use the gui environment,right-click the directory which has
"myfile" in it,then choose "open as administrator",open the
directory,then right-click "myfile"->properties->permissions,then
change the own by mouse.Nothing happened....
So,gnome do not invoke the syscall?