[if every] grouping not working

I’ve copied out this code from the manual, but for whatever reason it refuses to display properly:

[loop type=post]
  [if every=5 first=true]<div class="group-container">[/if]
  [field thumbnail]
  [field title]
  [if every=4 last=true]</div>[/if]
[/loop]

It seems to work if I remove first=true, but then that defeats the purpose. I’ve tested it by replacing the div class with an <h4>START</h4> and <h4>END</h4>. Here is my testing code:

[loop type=post]
  [if every=5 first=true]<h4>START</h4>[/if]
  <p>title: [field title]</p>
  [if every=4 last=true]<h4>END</h4>[/if]
[/loop]

And the result:

START

title: Gallery post format

title: Style guide

title: Another standard post

title: We understand our customers

title: Property law

title: On your behalf throughout the process

title: Post split into multiple pages, post parts

END

https://wordpress.org/plugins/custom-content-shortcode/