swipe keyboard code crash on back button

I'm noticed a problem with the swipe keyboard.
Here's how to reproduce.

1. create a new note ysing notify
   
2. edit the note
   
3. tap the screen to display the screen of swipe singles
   
4. press the physical button to go back.
   
   

the result if connected through the IDE is

         |_| espruino.com
 2v13.13 (c) 2021 G.Williams
Uncaught Error: clearInterval(undefined) not allowed. Use clearInterval() instead.
 at line 3 col 1881 in textinput
...clearInterval(flashInterval);Bangle.s­etUI();g.clearRect(Bang...
                              ^
in function "back" called from line 1 col 8
b.back()
       ^
in function called from system
>