Charset.VerifyFile always returns 0

I'm trying to check whether a file has been saved with UTF-8 encoding (with/without BOM/preamble) but in my tests .VerifyFile always returns 0.

ActiveX | v9.5.0.60

sFilePathLocal = "e:\temp\test.txt"

with Server.CreateObject("Chilkat_9_5_0.FileAccess")
   .WriteEntireTextFile sFilePathLocal, "abc-£-123", "utf-8", 1
end with

with Server.CreateObject("Chilkat_9_5_0.Charset")
response.write .VerifyFile("utf-8", sFilePathLocal)
end with