Some lines of vertor graphics dissappear while scaling with ViewBox

Question

I've draw some picture at Expression Blend with a quite big size. It's approx. 8000x1200 unit. When I scale it down at Expression Blend to fit in on screen all lines is visible. At link bellow you can see a screenshoot.
http://i073.radikal.ru/1005/bc/5c06addcc30c.png
But when I scale this picture using ViewBox some lines dissappear. It looks like this:
http://s09.radikal.ru/i182/1005/45/80192b60e9ff.png

How can a scale large pictures at ViewBox without loosing the elements?