If I may expand on it a bit, with SCIM on and XKB layout switching set to CTRL+SHIFT, there are 3 contenders for CTRL+SHIFT, and they supersede each other in this order:
1. XKB
2. SCIM
3. Application's CTRL+SHIFT-<key> shortcuts
The patch from FreeDesktop.org bug #865 fixes it so that 1 (XKB) no longer blocks 3, but it still blocks 2 because CTRL+SHIFT release is eaten by XKB and SCIM doesn't see it. I think its OK as you wouldn't want to assign the same shortcut key to both keyboard layout and SCIM.
If I may expand on it a bit, with SCIM on and XKB layout switching set to CTRL+SHIFT, there are 3 contenders for CTRL+SHIFT, and they supersede each other in this order:
1. XKB
2. SCIM
3. Application's CTRL+SHIFT-<key> shortcuts
The patch from FreeDesktop.org bug #865 fixes it so that 1 (XKB) no longer blocks 3, but it still blocks 2 because CTRL+SHIFT release is eaten by XKB and SCIM doesn't see it. I think its OK as you wouldn't want to assign the same shortcut key to both keyboard layout and SCIM.