[Plugin: WP-Infobox] Infobox appears in post and in top of page

I am having a problem using the WP-Infobox plugin. The plugin worked fine for a few days after install, but after I turned on the show featured image option in my Arras theme it started showing up in the top right corner (as you can see here: http://film-mag.net/wp/wp-content/uploads/2012/03/infobox_bug.jpg)
I used to fix this problem on the older versions of WordPress by adding a “thumb” before in the custom fields box, but now not even this helps.
It’s even worse when I try to insert a picture; then the infobox is duplicated all over the place (in the sidebars, etc). In fact, older stuff I put into previous infoboxes appear as well.

This may be related to another problem I’m having with event calendar about which I will make another post here so as to keep things clean if they are not related (I will link later). EDIT: Here is the link

Can anyone please suggest what to do? Thank you!