Faulty assert in BarSeries.java disalows the inclusion of negative values on chart
First image: tooltip works for positive values.
Second image: tooltip does not work. Value represented by bar is hard to visualize due to the fact that the numeric axis does not show negative values.
Third image: assert statement eliminates the ability to shift the minY value of the numeric axis to include negative values
Edit: pardon the misspelling of "disallows" in the title.
Sencha - GXT Dev Team
The assert was added because mixing of positive and negative values in bar series are not supported as of the 3.0 release. However, this is a planned feature in a future release.