I’ll post this here because this is exasperating and I don’t know what to do anymore.
Almost exactly a year ago I sent this bug report, and it’s been closed at least twice as “By design”. The behaviour is NOT by design, it’s a BUG.
If, for example, there’s a class named Thing and another named thing (simplified example etc etc), doing AssetDatabase.FindAssets("t:thing") will only find the assets of type thing and not the assets of type Thing. And searching for “t:Thing” will not find ANY of the assets.
If, as the resolution notes say, “searching is case-insensitive”, then both search queries should find ALL the assets, of both type thing and Thing. If searching was case-sensitive, it would find assets with both queries.
That is a bug, I don’t know how to explain it anymore.