Filter not applied in template?

[Foeth]

In a mailtemplate that im building im putting the following Hubl code (simplified): 

<p>{{ deal.hubspot_owner_id.firstname|lower }}</p>

I would expect this to result in a full lower case string displaying the firstname of the owner, except that it doesnt; when i send the email from the workflow, it shows "Michel" as the firstname. 

What am i doing wrong?

[Foeth · Accepted solution]

Nevermind, apparently this is not supported in emails: (from the docs)

Please note that using filters on any personalization variables (such as but not limited to contacts, company, and deal variables) is not currently supported for email in HubSpot due to how emails are rendered. Filters can be applied to these properties on HubSpot CMS page and blog templates.