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This is a logic errors bug
The wrong operator, an inverted condition, a formula the right way round but backwards.
String comparison is case-sensitive: "A" and "a" are different characters to Python. The check only lists lowercase vowels, so every capital vowel is skipped, and the bug only shows on input with capitals, which test data often lacks. Normalise case before comparing, with text.lower() once, rather than listing both cases. The same bug hides in username checks, search and answer marking: anything that compares text a person typed.
The pattern behind it: logic errors.
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<iframe src="https://trybughunt.com/embed/90badc40-7bae-4a28-a9fa-77254940e205" title="Debugging challenge: Vowel counter skips capital letters" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe>
<p style="font-size:14px">Debugging challenge from <a href="https://trybughunt.com/challenges/90badc40-7bae-4a28-a9fa-77254940e205">BugHunt</a></p>