wf.Contains has a bug

[rockyhan]

texts := []string{
"Miyamoto Musashi",
"妲己",
"アンジェラ",
"ความรุ่งโรจน์",
}
wf := wordsfilter.New()

// Generate
root := wf.Generate(texts)

c1 := wf.Contains("妲己", root)
// c1 true
c2 := wf.Contains("Morning 妲己", root)
// c2 false

Why c2 is false?