If by tearing you mean leaving artifacts on the screen, differences in behavior are almost certainly due to different versions of Tk being used.  Tkinter is really just a wrapper around calls to Tk; nearly all of the heavy-duty graphics work is done by Tk making calls to other, platform-specific graphics libraries.  FWIW, I ran your last test with the current python.org 2.7.8 and 3.4.1 on OS X with the current ActiveTcl Tk 8.5.15 and they both performed identically: I expanded the frame to fill the screen and could cleanly move the slider to the left or right with no artifacts.