In the following examples of using past conditional in Portuguese:
Se tivesses embarcado com o Vasco da Gama para Índia, ías ver...
Se eu soubesse que havia un temporal tinha atravessado a ponte mesmo a pé.
only one part of the conditional phrase uses mais-que-perfeito, whereas the other uses pretérito imperfeito. Assimil then notes that the seeming violation of the seeming violation of the time agreement (see sequence of tenses) is quite normal for Portuguese:
Mais le portugais exige seulement que l'un des verbes marque le temps. (But the Portuguese requires only one of the verbs to show the tense.)
Is such liberty in using tenses a general feature of Portuguese or are there finer rules governing the use of tenses in complex sentences? Doesn't it introduce ambiguities when a (long) sentence starts in one tense, but then suddenly moves deeper into to the past? Are there examples of exploiting such confusions (e.g., in witticisms or idioms)?