Odd highlighting of the atom 'is'

[Anniepoo]

1. Open
   https://swish.swi-prolog.org/p/is_highlight_demo.swinb

2. Run the query
   EXPECTED: a list
   OBSERVED: list has is oddly highlighted- parens around it, and it's blue.

This is confusing for students. I've no idea why it's occuring.