Gmail and Labels: label correspondig to folder not added to header?

[rionda]

General informations

• system/distribution (with version): MacOS 10.15.6
• offlineimap version (offlineimap -V): offlineimap v7.2.1, imaplib2 v2.57 (bundled), Python v2.7.18, OpenSSL 1.1.1g 21 Apr 2020 (that's what comes with MacPorts)
• Python version: Python 2.7.18
• server name or domain: Gmail
• CLI options: none

Configuration file offlineimaprc

[general]
accounts = MyAcct
ui=ttyui

[Account MyAcct]
localrepository = MyAcctlocal
remoterepository = MyAcctserver
# Sync the labels
synclabels = yes
# Header where labels go (X-Keywords is the default, but mutt uses X-Label)
labelsheader = X-Label
# Ignore some Gmail labels
ignorelabels = \Sent, \Draft, \Spam, \Trash, \Important
# Update notmuch database after syncing
postsynchook = notmuch new

# This is the remote repository
[Repository MyAcctserver]
type = Gmail
# Private auth info removed
# Ignore some folders
folderfilter = lambda foldername : foldername not in [ '[Gmail]/Important', '[Gmail]/All Mail'] and foldername[:3] != "Old"
# Remap some labels. It must match with the entry in the local repository
nametrans = lambda folder: {'[Gmail]/Drafts':    'drafts',
                            '[Gmail]/Sent Mail': 'sent',
                            '[Gmail]/Starred':   'starred',
                            '[Gmail]/Important':   'important',
                            '[Gmail]/Spam':   'spam',
                            '[Gmail]/Trash':     'trash',
                            '[Gmail]/All Mail':  'archive',
                            }.get(folder, folder)

# This is the 'local' repository
[Repository MyAcctlocal]
type = GmailMaildir
localfolders = ~/Mail/MyAcct
# Put different IMAP folders in separate directories
sep = /
# Ignore some folders
folderfilter = lambda foldername : foldername not in [ '[Gmail]/Important', '[Gmail]/All Mail'] and foldername[:3] != "Old"
# Remap some labels. It must match with the entry in the remote repository
nametrans = lambda folder: {'drafts':   '[Gmail]/Drafts',
                            'sent':     '[Gmail]/Sent Mail',
                            'important':'[Gmail]/Important',
                            'spam':     '[Gmail]/Spam',
                            'starred':  '[Gmail]/Starred',
                            'trash':    '[Gmail]/Trash',
                            'archive':  '[Gmail]/All Mail',
                            }.get(folder, folder

Steps to reproduce the error

• Add two labels, A and B to a message in inbox.
• After syncing
  • a copy (?) of the message is present in the folder A. The X-Label header contains only the labels B and \Inbox (to be precise it's X-Label: B \Inbox);
  • another copy (?) of the message is present in the folder B. The X-Label header contains only the labels A and \Inbox (to be precise, its X-Label A \Inbox);
  • a third copy (?) of the message is present in the inbox. The X-Label header contains only the labels A and \Inbox (to be precies, it's X-Label A B);

I would be expecting the header (of all copies?) to contain all the labels. I believe I expect this behavior because folders are labels in Gmail, and viceversa, so it just seems more natural to have all the labels in it. On the other hand, I understand that what seems to be stored are the "additional" labels: the fact that the message is in this folder implies that it has the label corresponding to the folder.

Is this expected behavior from the program or is it a bug? Perhaps it could be tunable? (I couldn't find in the code where the "folder" label may be removed).

Thanks.