Also this used to enable a significant negative vote weight effect. Where voting for your preferred party with your second vote could actually make them lose se

Also this used to enable a significant negative vote weight effect. Where voting for your preferred party with your second vote could actually make them lose seats if your party had more overhang mandates through direct first votes than through the proportional second vote. This was ruled unconstitutional by the Bundesverfassungsgericht in 2008 and the law was eventually changed. The current voting law in effect in 2013 reduced the effect but it's still there. So to balance those overhang seats, balancing seats are introduced which might increase the number of total seats beyond the originally intended number by quite a significant amount. http://en.wikipedia.org/wiki/Negative_vote_weight http://en.wikipedia.org/wiki/Negative_vote_weight