Switching the toolbar icons from just "icons only" to "icons and text" will cause the website settings icon to shrink and eventually disappear.
See video:
(The quick fix is to just close out of your browsing session. This will reset the icons. Still not ideal, of course).
I expect the icons to not shrink incrementally when switching back and forth from "icons only" to "icons and text" and for me to not need to close out the browsing session just to reset the icon.
Version 0.99.130.3-rc (WebKit 621.1.2.111.4)
Sequoia (15)