When defined a Keyword list for Data Protection rule, even if Keyword item has Full-width(Double byte) character, the rule is triggered by both Full-width and Half-width(Single byte) character in email. And vice versa.
Data Protection Keywords or Regular Expressions list does not distinguish Full-width and Half-width for some characters.
As a workaround, please consider other detection rather than sequence of the specific character in Subject or Body. Such as email header values could be alternative.
Broadcom is aware of this issue and will update this document when a solution becomes available. It is not necessary to log a support case on this issue.