evil-tabs breaks scroll-preserve-screen-position

[troyp]

When a window has evil-tabs' tab bar at the top, scroll-preserve-screen-position loses track of the line number.

• version: From Github repo, on May 17, 2015
• to reproduce: In a window with the evil-tabs tab-bar at the top, perform the following steps:
• execute (setq scroll-preserve-screen-position 'always)
• press PageDown
• press PageUp
• what should happen: the cursor should return to its original column
• what does happen: the cursor returns a line above its original position. It may also return in the wrong column (with one window, it returns to the first column; in the left window of a vertically split frame, it retains the correct column).
• notes: Pressing PageUp, then PageDown also gives an incorrect result, although it seems less predictable.