Why is my Compose key not being passed to Synergy?

The key that I assign to the compose key (right Alt) is not passed to the remote computer by Synergy. I don't know if it's a problem with Synergy or with X, but my guess is that the compose key is 'eaten' by X before Synergy can get it. How can I check if this is correct? If so, is there a way to both use the key for composing and pass it to Synergy? ----- Following the instructions from slm, I get the results below. So the compose key is caught by Synergy, but the id and the onKeyUp mask are different. When right Alt is defined as a compose key: new mask: 0x2000 event: KeyPress code=108, state=0x0010 onKeyDown id=61216 mask=0x2000 button=0x006c send key down to "tapioca" id=61216, mask=0x2000, button=0x006c new mask: 0x2000 event: KeyRelease code=108, state=0x0010 onKeyUp id=61216 mask=0x2000 button=0x006c send key up to "tapioca" id=61216, mask=0x2000, button=0x006c When right Alt is not defined as a compose key: new mask: 0x2000 event: KeyPress code=108, state=0x0010 onKeyDown id=61418 mask=0x2000 button=0x006c send key down to "tapioca" id=61418, mask=0x2000, button=0x006c new mask: 0x2004 event: KeyRelease code=108, state=0x0018 onKeyUp id=61418 mask=0x2004 button=0x006c send key up to "tapioca" id=61418, mask=0x2004, button=0x006c