Might want to include your system specifications too for this to be resolved, and also, have you made sure you have current video drivers installed for your video card?

Are you by any chance opening and closing the startmenu rapidly?

Also does it happen if you have the taskbar at the bottom of the screen?

I will post my system specs when I get home....

No, not opening it rapidly... Just clicking the button with my mouse, or pressing the windows key on the keyboard. Then just leaving it open, without doing anything else, i can watch it flicker somewhat regularly. 

Yes, it also flickers if the taskbar is at the bottom. I haven't seen the stretching issue when at the bottom, but I really didn't check for that yet.

As you can see in the earlier picture the items on the right side of the menu are missing below "Games".  It mostly starts from there, then appears to redraw each menu item, one after the other (occasionally it does this with more or even all the right-hand menu items). But it does it quickly, it only takes about a second to do all of them. Then it continues to repeat over and over, as long as the start menu is open.