[galaxy-dev] bed 12 to bed 6 while displaying galaxy tracks on UCSC

Hi, I have a question. While trying to view bed tracks on UCSC by clicking on display at UCSC_main, the data on URL used to upload on UCSC: http://galaxy/root/display_as?id=8155&display_app=ucsc&authz_method=display_at was of bed 6 format. I am intrigued since the original data at galaxy history page with which we use to view at UCSC is of bed 12 format. Can anyone explain why this happened? Thank you so much!