Mail Tags Escaping brackets

I’m trying to use Mail Tags in the Mail section on the admin screen, and In the Subject: line i’m trying to use MainSubj [SubSubj] where the subject should show up as something like “[Suggestion] This is suggestion”. However instead what happens is I get: “[MainSubj] This is a suggestion”. I’d like to actually have those pair of brackets in the email subject. Do I need to escape them with something? Thanks.

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