It seems to me that Magazine Basic causes some problem in the number of words in RSS feed. I find, that the number of words displayed in the excerpt in the RSS, is larger than the default WP excerpt limit. And I am unable to find how that is happening - but it is happening in Magazine Basic
For example, in a multisite installation of WP3,
RSS in excerpt mode (Magazine Basic)
RSS in excerpt mode (other theme)
There is no configuration difference between the two 'sites' - except for the difference in theme.