Conversations not imported from phpbb

Affected version
xf 2.1, xfi 1.3.2


When running the import from phpbb 3.2, conversations are not imported as conversations but rather as single private messages.

PHPBB stores the information about conversations in the phpbb3_privmsgs tables with a parameter called root_level.

If root_level is 0 than it is the start of the new conversation.
Otherwise, root_level contains the message ID of the first message in the conversation. All subsequent messages in the same conversation hold the same number in root_level.

I assume it is possible for the importer to scan all PM's, if the root_level is "0" to start a new conversation. Scan to see if there are other messages where the root_level is the message_id of the above post. If yes, they belong to the same conversation.

I would be happy if this can be fixed in the importer.