In multisite, user capability not working?

My site is mutltisite.

Master site is http://www.master.com, and sub site is http://www.aaa.com.
Among them, http://www.aaa.com administor is http://www.master.com create user.

In http://www.master.com admin, i print_r:

global $current_user
print_r($current_user->allcaps);

result:
Array
(
    [switch_themes] => 1
    [edit_themes] => 1
    [activate_plugins] => 1
    [edit_plugins] => 1
)

And i print_r current_user_can( ‘activate_plugins’ ), it return me bool(false).

How is this going?