Highlighting media assets in timeline when not wanted

Hi, editing SD MXf 50, files, have been for ages, now the new version highlights the media that the cursor is over whenever you hit play, arrow or spacebar. Also does it when I skip to the next clip with the up/down keys.Locking the tracks stops it, but I need to edit them.Very frustrating as it can lead to moving media in the timeline when you dont want to. Is this a feature i can turn off or a bug? Cheers, J.