I have a Drupal 7 installation, multilingual. No matter which input format i'm choosing for the node body, every HTML tag is stripped. The input format is well configured. It's like Drupal always uses Plain Text as Filter, even if Full HTML is selected.
I found the answer in the Drupal Forum: https://drupal.org/node/1829860
For the records: After some searching I found the culprit: I defined a custom display setting for the content type article (/admin/structure/types/manage/article/display) and changed (by mistake) the field format to "plain text" for the body text. Reverting to "default" fixed the problem.