To temporary resolve the "Unable to close Trackpad Handwriting with Control
ShiftSpace" until Apple release a fix, try this:
1. Open a terminal screen before launching Trackpad Handwriting
2. Launch Trackpad Handwriting
3. Try to close it, but failed
4. Switch to Terminal session using "Command+tab"
5. Find the process id of "Finder", command is "ps -aef|grep Finder"
6. the second number in the line is the process ID
7. Restart the Finder process by "kill -HUP xxxxx", where xxxxx=process id
8. This will issue a soft restart of Finder and now you can close the Trackpad Handwriting by "Control
ShiftSpace"
PS. if you didn't have an active Terminal session when Trackpad stuck, use "Command
ShiftU" to open Utility folder, select Terminal, launch it by "Command+O". Then continue with Step 5.
Hope this helps.