Update: it is clear now that I misinterpreted the rule. (In my defense, the linked story presents the matter less than clearly.) See the comments for clarification.
Mexico votes Sunday for president and all members of both chambers of the federal congress.
The Chamber of Deputies election has an interesting ballot format. The Deputies are elected by a Mixed-Member Majoritarian system (with caps–more below–but it is not MMP). Unlike most mixed-member systems, the voter has only one vote. The vote for a candidate in any given single-seat district also counts for the party list; that is, there is no separate list vote.
Candidates are sometimes nominated by pre-electoral coalitions. However, the parties keep their separate ballot identities. A vote is valid even if the voter marks the ballot for two or more parties in coalition. However, such a vote would count only for the candidate, and not for any of the parties’ list. This is an unusual provision, and I am not aware offhand of anything similar elsewhere. (See earlier thread, and comment by Manuel, in which this feature was mentioned.)