Hello,
It appears to be fine on other pages so I could narrow this down to two things.
a) Something specifically on the page, whether an extension or script is causing the onclick to redirect improperly
b) Something in your servers SEF settings for URLs is not set properly. You can try the tutorial here to see if that helps:
http://www.shape5.com/component/option,com_smf/Itemid,75/topic,35973.0/