The article presents analysis of a Polish Internet political discussion forum, characterized by significant polarization and high levels of emotion. The study compares samples of discussions gathered at three periods during a 2-year time, during which events occurred that significantly increased the already strong political division of Polish society (the sudden death of the President in a plane crash, snap elections, accusations of assassination and treason). Despite these circumstances, we observe a remarkable stability of individual political support. Extensive discussions among the forum users did not lead to changes in their political affiliations or specific opinions. In contrast, emotions expressed by the forum users, mainly negative, were found to vary from post to post and between the discussion threads. An automatic emotion recognition algorithm is presented, giving results closely corresponding to human evaluations. The authors also show that differences in a user interface between the two alternative forum webpages, especially effects of features promoting direct one-to-one communication, have significant impact on message content and decrease negative emotions. Implications of such changes on promoting communication across a political divide are discussed.