Not opposite meanings, but opposite T-V attitudes: "Vos", second person pronoun, is very informal in those regions with 'voseo' (eg. Argentina), and very formal in other regions (Spain). This latter form, though, is seldom used (it's rather archaic), and hence there is little chance of confusion. One case I recall: "Jesús, en Vos confío" a traditional Spanish christian jaculatory (very short prayer; "Jesus, I put my trust in you") is said verbatim in Argentina, and most people here believe wrongly that the informal "voseo" is used...
PS: This other confusion is not from regional context, rather from the technical, but I experienced it just now, listening to the radio about the "Costa Concordia" shipwreck:
Rumbo : its common meaning is "course" (direction, of a vehicle, a ship...), but in naval/marine context it has a specific technical meaning: a dangerous hole in the hull of the ship. So, if you are aboard and happen to hear "¡Tenemos un gran rumbo!"... perhaps you'll think that it's good news, when actually it's very bad.