The pronunciation issue you're referring to is related to the different nature of the languages as far as rythm is concerned. Brazilian Portuguese is a syllable-timed language, which means that each syllable takes about the same time to be pronounced. On the other hand, English is a stress-timed language, which means that the interval between stressed syllables is approximatly the same. Because the stress in English is so irregular (the words that carry more important meaning tend to be stressed more often), some words are compressed during natural speech.

For more information about rythm, read the following page:

http://www.sk.com.br/sk-reduc.html

Tiago