canvas only updates after tab/window switch

Hello,

NoScript prevents the canvas element from showing changes until you switch to another window/tab. The script below
demonstrates it. It has an onclick handler for the canvas element that pushes the clicked location
into an array an then orders to redraw the canvas with all points recorded so far. So basically each click should add a point
to the canvas. If NoScript is enabled, however, the canvas won't be redrawn (but all JS is executed!) until you switch to
another window/tab. After the switch it will continue to work properly.

Code: http://pastie.org/private/xjur0j5goyjrzaovrqxfa
To test it: http://pastehtml.com/view/cdd0eeyxw.html

Greetings,
FrankD