I have a tag that is displaying in question lists in faded form as if it is one of my ignored tags, but it isn't.
I had it as one of my ignored tags for quite a while, but as I started using the app recently I "unignored" it some weeks ago.
The hover card shows a silver star like all of the other non-favorite, non-ignored tag, and the tag does not appear in the list of ignored tags.
So, I can only conclude that this is a bug. Perhaps some bit of data got left over when I removed the tag from my ignore list.
If it matters, the tag is trello.