I was experimenting with face definitions and created a number of "test" faces that were meant to be temporary. At the end of the experiments, I wanted to clean up after myself, so I attempted (unintern FACE), but the faces remained on the return value of function (face-list). My guess was that the faces are stored in a different obarray. Then I looked at the function definition for (face-list) in file faces.el, and it gets its data from variable face-new-frame-defaults which is defined in C source code, which is a simple list, and not seemingly updated.

As a complication to testing and debugging, the doc-string for unintern indicates that FACE can be specified either as a string or as a symbol. However, the function behaves differently for the alternatives. This is kind of a tangent, and may be a bug in unintern, but it confused debugging my situation. For a normal symbol (setq my-temp-test-symbol "HELP!"), performing unintern with a string argument correctly returned t on symbol-found-and-uninterned and nil on symbol-not-found; However, when passed a symbol 'my-temp-test-symbol, it returned t repeatedly.

For faces, performing unintern with a symbol argument always returns t, and with a string argument does first return t, and then nil, but the face continues to appear in the output of (face-list).