That is the windows default. CRTL+SPC = Turn Chinese IME on 101 keyboard on or off
You can change the key combination for switching between languages or keyboard layouts in the Advanced Key Setting dialog box. To open the Advanced Key Setting dialog box, right-click the Language bar, and then click Settings. Under Preferences, click Key Settings.
Put another shortcut instead of CRTL+SPC. Then you can use CRTL+SPC as you wish.