i18ntaxonomy_db_rewrite_sql breaks Pathauto on synchronisation

Using i18nsync and i18ntaxonomy breaks the automatic generation of url aliases by Pathauto, specifically when using a token like [termpath] or [termpath-raw].

The Condition

Assume the following conditions:

• you have translated nodes
• you have hierarchical taxonomies and translations thereof
• you let Pathauto automagically generate url aliases using tokens like this: [termpath]/[title]
• you use i18nsync to synchronize some fields between translated nodes

The Error

Lets say that you are editing a node which has translations and your current interface language is English. When you save the node after an edit, i18nsync will synchronize the translations as configured. The synchronization causes each translation to be loaded (node_load), synchronised and saved again (node_save). Saving the node after a sync causes Pathauto to regenerate/update the url alias. Remember that we have translated taxonomies, so that the result of [termpath]/[title] will depend on the translation of taxonomy term assigned to a node. At some point Pathauto will do
$parents = taxonomy_get_parents_all($category->tid);
(pathauto.module 6.x-1.2 line 129)

taxonomy.module line 755 in turn will do this:
$result = db_query(db_rewrite_sql('SELECT t.tid, t.* FROM {term_data} t INNER JOIN {term_hierarchy} h ON h.parent = t.tid WHERE h.tid = %d ORDER BY weight, name', 't', 'tid'), $tid);

this again will trigger hook_db_rewrite_sql implemented by i18ntaxonomy (i18ntaxonomy_db_rewrite_sql in i18ntaxonomy.module line 292). The rewritten query will look like this:

SELECT t.tid, t.* FROM {term_data} t INNER JOIN {term_hierarchy} h ON h.parent = t.tid   WHERE (t.language ='en' OR t.language ='' OR t.language IS NULL) AND (  h.tid = %d )ORDER BY weight, name

Note the WHERE clause that filters for taxonomy terms that are not in the current language or don't have a language assigned and are therefore presumed language independent.

If the term of the node that is currently processed is French, then Pathauto will be looking for ancestor terms of that French term, but i18ntaxonomy will filter them all out, because, reasonably enough, the terms ancestor terms are all in French.

Possibly a Solution

I noticed that i18ntaxonomy_db_rewrite_sql calls 18n_selection_mode which is in i18n.module line 348. The description says

Allows several modes for query rewriting and to change them programatically.

I imagine a solution would be to set 18n_selection_mode to

off = No language conditions inserted

for the duration of the sync and afterwards setting it back to what it was. I will try this at home :-) and provide a patch if it leads to success.