To make some sense out of this behavior:
The RadNumericUpDown parses the text as follows:
.TryParse(text, NumberStyles.Any, formatInfo,
It uses "NumberStyles.Any", which inspects the formatInfo.
Like Vladi mentioned, if your formatInfo does not contain information on "CurrencyDecimalSeparator" and "CurrencyGroupSeparator", CurrencyGroupSeparator will default to comma.
That's why the parsing, and thus the control, will still accept commas.
The issue is in the parsing using "NumberStyles.Any".
It should take into account the "ValueFormat" property of the RadNumericUpDown, and use
"NumberStyles.Number", "NumberStyles.Currency" accordingly in the parsing.