Easy, your monitor according to the specs is "1920 x 1200 pixels" not the 1920x1080 you think it is, it just runs at that resolution. (taken from here) http://www.pcworld.com/product/546524/hz281hpb-black-27-5-quot-widescreen-lcd-monitor.html
Combine that with these key factor from the avermedia site.
" The Live Gamer HD does not work with 1920*1200 monitors." Taken from here, http://www.avermedia.com/product/ProductDetail.aspx?Id=571
Therfore, your capture card does not support your monitors resolution and drops down to the next lowest compatible available resolution. Record in that resolution or get a monitor or a capture card that supports your monitor.