As my "day job" I am a manager at an internet company and am very familar with referrers but I have never seen "blank entries" on multiple lines. If two lines have no referer then they traditionally are grouped together as "Bookmarked" or similar labeling.. Some system strip out the data when the hit comes from the site where the page is also on (ie may not show hits from Instructables.com) as it is an internal link not an external referrer but on my lists of referers for my instructables I usually see "instructables.com" being listed but at a far lower "hit" amount than would be expected. I have also had cases where I posted my project on Pinterest then clicked on the pinterest link (to test it) but a pinterest referral did not ever show up on the list.

If the blanks were other people tweeting then they should also be listed under t.co as is standard for referrers and that does not explain the first entry in my list which was also blank?

that makes more sence about the instructables redirect... thanks..

hope someone else can shed some light on the blanks..