The custom spell was named Ice Dart (the underlying spell was Death Dart).

As documented here, I am unable to refund the spell viewtopic.php?f=10&t=2163&p=14167#p14167
I went to Axis Mundi to revert the Custom Spell to its original name - but it doesn't appear in the dropdown.
The expected behaviour is that I can revert "Ice Dart (Death Dart)" to vanilla Death Dart.

I think this might be something to do with the custom name "Ice Dart" overlapping the real Ice Dart spell.
My recommendation is that custom spells shouldn't have real spell names available as options when renaming, to avoid cases like this.
(I'd also really like a way to refund the fake Death Dart