Custom field code is not translated in email template

I’m running InvoicePlane 1.5.2 and would like to use custom fields in my email templates.
I created some fields and inserted them into the template. They look like {{{ip_cf_8}}} {{{ip_cf_9}}}.
However when i send the e-mail, the code is not replaced by the content of the fields.
Is this a known issue or am i doing something wrong in creating or inserting the custom fields in the email template?

I just upgraded to 1.5.2 and I’m having the same issue.

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