Personalization Tags in custom html via API getting encoded and not replaced on send

[JonathanN736]

We are uploading html_content via the create/update endpoints for campaigns

POST /emails and PUT /emails/activities/{campaign_activity_id}

We have links within our html that use custom fields as params.

ex.

<a href="https://mywebsite.com?custom_param=[[custom.custom_attr]]">Cool Link</a>

Our problem is the brackets in anchor tags are being url encoded.

ex.

`<a href="https://mywebsite.com?custom_param=%5B%5Bcustom.custom_attr%5D%5D">Cool Link</a>`

So, when the email is sent the value isn't replaced.