Metacity doesn't handle KeyRelease event for Super_L

Using Breezy updated to this moment,
here is a description to get to the problem:

1. Go to Keyboard Preferences -> Layout Options -> Alt/Win key behaviour
2. Select "Super is mapped to the Win-keys (default)."
3. Go to Keyboard Shortcuts -> Window Management -> Move between windows with popup
4. Click on it to modify
5. Press Left Win key followed by Tab while still pressing the Win key. It
should read: <Mod4>Tab
6. Use Mod4+Tab as Alt+Tab

It doesn't work the same way as Alt+Tab yet it should. I'd like to free Alt for
other uses.

xev(1) reports for Alt:

KeyPress event, serial 29, synthetic NO, window 0x3200001,
    root 0x4c, subw 0x0, time 1172134, (270,674), root:(1130,758),
    state 0x0, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
    XLookupString gives 0 bytes:
    XmbLookupString gives 0 bytes:
    XFilterEvent returns: False

KeyRelease event, serial 29, synthetic NO, window 0x3200001,
    root 0x4c, subw 0x0, time 1173005, (270,674), root:(1130,758),
    state 0x8, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
    XLookupString gives 0 bytes:

and for the Left Win key:

KeyPress event, serial 29, synthetic NO, window 0x3200001,
    root 0x4c, subw 0x0, time 1235469, (103,133), root:(963,217),
    state 0x0, keycode 115 (keysym 0xffeb, Super_L), same_screen YES,
    XLookupString gives 0 bytes:
    XmbLookupString gives 0 bytes:
    XFilterEvent returns: False

KeyRelease event, serial 29, synthetic NO, window 0x3200001,
    root 0x4c, subw 0x0, time 1238372, (103,133), root:(963,217),
    state 0x40, keycode 115 (keysym 0xffeb, Super_L), same_screen YES,
    XLookupString gives 0 bytes:

thus X seems to get the KeyRelease event nicely for both keys while metacity
doesn't.