I think the answer to this may be that OBV is constructed by using an arbitrary starting value, and BigCharts constructs the indicator from scratch on each chart. Notice on both of your charts that the OBV starts at zero.
Now the short term chart shows OBV at zero at it's beginning on the first day of January, 2003. But if you look at the longer term chart, you will see that the OBV is -0.5 on the first day of January 2003! This is because the OBV value is constructed in the context of SPECIFIC CHART that you're looking at.
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