When trying to map a key to semicolon (Punctuation → Semi Colon ;, ;:) the actual key saved is comma instead (,<). This makes it impossible to create a layout with semicolon in it using the app.
The workaround is to edit the layout .txt directly and map to the token scolmanually (see SmartEngine Supported Actions PDF). E.g. to map closing square bracket to semi colon:
layout1.txt
<base>
[cbrk]>[scol]
<keypad>
<function1>
<function2>
<function3>