RSS feed by tag and/or category broken

Hello,

I’m having problems with my site showing tag and/or category specific rss feeds.
The problem is that all my posts are being shown, it doesn’t matter if I specify a tag like this:
http://www.mysite.com/tag/exampletag/feed/
or http://www.mysite.com/category/examplecategory/feed/

If I go to http://www.mysite.com/tag/exampletag/ I get only the posts with the exampletag tag set.

Anyone got any idea what could be causing this? Like if there are things in the loop that could disturb something somehow.