weird wear pattern

After a blast up the putty road yesterday I was inspecting the wear on my rear tyre. Normal feathering/balling was present from edge to edge. However, the top was smooth (expected from highway riding) and two bands an inch wide at 10 and 2 o'clock. So, smooth-feathered-smooth-feathered on each side. WTF? I dont tend to ride for long distances half keeled over on each side?
Has anyone seen this before and is it normal or is it telling me something about my setup?
Has anyone seen this before and is it normal or is it telling me something about my setup?