Hurray, thank you!

It does reproduce for me on 1.32.0 using the Vector skin. Did you try going to "Recent Changes"? That's where I see the "Atom" link in the left sidebar with an orange RSS icon. I don't see it on other pages.

Saper has updated here, with added testing:

I raised the priority of this task from Low to Normal. A documented feature ($wgFeed) clearly fails to work. This is a bug fix, not a feature enhancement. The bug has been encountered in actual usage by different people. Someone made the effort, long ago, to create this task and provide a solution. Someone else studied the solution and expressed approval. I've brought it up to date with changes that occurred in the meantime. Following through and merging the solution, before it gets out of sync with the master branch again, can't reasonably be considered a low priority.

Change 247821 was written before the addition of the hook AfterBuildFeedLinks. In order to make the equivalent change now, it's necessary to decide whether AfterBuildFeedLinks should be called unconditionally, or only when $wgFeed is true.

Until the bug is fixed, a workaround for hiding the Atom link in the sidebar of the RecentChanges page is to make these arrays empty in LocalSettings.php:

Patches were submitted to fix this bug a year and a half ago, but never merged. The bug still exists. What needs to happen now? Can I help?