Mailman incorrectly removes allowed attachmens when Collapse alternatives is set

mailman: 3.3.10

Collapse alternatives: yes

Sending mail with following structure

("text" "plain" ("charset" "UTF-8") NIL NIL "7bit" 4 0 NIL NIL NIL NIL)("application" "octet-stream" ("name" "var-expand.patch") NIL NIL "base64" 804 NIL ("attachment" ("filename" "var-expand.patch")) NIL NIL) "mixed" ("boundary" "----=_Part_2323_1133611924.1739791120600") NIL NIL NIL

causes the attachment to be dropped even if it's whitelisted with

pass types:

multipart/mixed
multipart/alternative
multipart/signed
text/plain
text/html
application/pgp-signature
application/octet-stream

pass extensions

patch
diff
asc
sig

I would've expected that the patch would've passed through.