Vertico distorts email attachments

[nameiwillforget]

When I use C-c C-a in Gnus with Vertico to attach, say, a plaintext file, I receive the following output:

<#part type=#("text/plain" 0 10 (fontified nil)) filename="~/gdb.txt" disposition=inline description=gdb>
<#/part>

This triggers this error:

smtpmail-send-it: Sending failed: 554 5.0.0 Error: failed to parse message: failed to get content type for for child 0:mime: expected slash after first token in response to .

When I turn off Vertico, it removes the brackets around the type description and sending the email works.