I found an interesting behavior of lineWidth on Opera when setting its value very large:
context.lineWidth = 222;
This is a rectangle whose lineWidth is 222!
On Google Chrome, Firefox or IE – it doesn’t act like Opera!
If you want to test it quickly, open my tool: Canvas Designer
Select “rectangle” from tool-box; set lineWidth=222 (from tool-box) and draw rectangle! (You must do this in Opera!)