2nd-3rd Language Carry Over

I learned French (poorly) in school 35 years ago. I then forgot all about it, hardly ever visiting French speaking countries.
When I started learning Spanish, 10 years ago, I noticed that when I was in a stressful 'conversation' I would start spouting (pretty poor) French. Over the years (thankfully) my Spanish has improved and my 'French ghost' has disappeared.

Portuguese and Spanish are similar, and in Portuguese there are all the sounds from Spanish.

Most of the brazilians can understand when Spanish speakers speak slowly (the biggest problem is the different words, and not listening skills). So learning portuguese will probably increase your Spanish listening skills.

Besides that, you can always try listening to songs or youtube videos in Spanish.

Good luck in Brazil.

Maybe general "listening skills" will improve and not get lost.You might have the impression you are picking up Portuguese easily because of the similarity in the languages (at least as written). My worry in your case would be confusing Spanish and Portuguese, especially at the beginning.

When I first started learning Spanish, I had a reasonable level in Italian, but was still learning. When I started Spanish, my Italian kept mixing in. Then, after concentrating totally on Spanish and leaving the Italian, I noticed I still understand Italian well but when I try to talk, it comes out in Spanish.

I don't know how much of this is linked to their proximity as languages and how much is a "box in the brain" that holds the languages in which we are not completely fluent, since I am not the only person this has happened to.

It depends on you as an individual. I speak excellent Spanish and get by quite well in Portuguese, after having spoken a lot of Portañol. If you have a keen ear, you will hear the differences between the two. If you don't, you will most likely mix them up.

The problem is of course I don't have a keen ear as discussed here:
http://www.lonelyplanet.com/thorntree/thread.jspa?newPost=true&messageID=19806085&#19806085

I will however be close to the Argentinian and Paraguayan borders and will travel over to those countries regularly to practise my Spanish!

PJ you will have trouble listening to Spanish @ Paraguay cos they mostly speak Guarani and or use lots of its words and the accent is totally different than the one of any other lat am country.

Yeah I agree the accent is tough but they generally use just Spanish in the capital and some of my mates can't even speak Guarani! I'll just have to do my best to improve through exposure to the language and hope that learning Portuguese helps too!

In my case, the problem occurs with Spanish, Portuguese and Italian. Not that much in listening skills but in speaking. Typically I can say 'obrigado' instead of 'gracias', or 'gracias' instead of 'grazie'. I don't have that problem with English or Russian, that I speak fluently. My skills in Spanish, Portuguese and Italian are much more limited. But, generally, if I mix up words that happens only within the same language group (romance in this case), never English and Spanish or Portuguese.