Bubble chart question

I suspect not many of you are using bubble charts, but I am trying to verify
whether I have a problem or if Excel does. Excel 2007 bubble chart using the
following data:

X Y Size
-16 -4 5
-13 -15 2
-8 0 3.5
-4 -19 3
-2 -10 4
0 -4 3
0 14 3.5
8 -19 4
9 5 2
11.5 -5 4

The X-axis data does not plot the negative values correctly, they are all on
the positive side. It appears that this feature preforms the same way in
2003. I realize that I can plot this using other chart types, but.... Any
comments would be appreciated.

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Cheers,
Shane Devenshire