SD Card issue in Rekordbox, slow read speed

In the attached video it shows the free scrolling of my collection, then it shows the slow jerky scrolling of my sd card class 6 (Link to sd card details  below)

Is this normal for other users? This never happened in the early versions of rb - But as of 1 update it turned into this

http://www.youtube.com/watch?v=7lX0mQHDs3A&feature=g-crec-u

http://www.verbatim-europe.co.uk/en_1/product_hd-video-sdhc-32gb-12-hours_23_0_15798.html