Darius - although you can mix positive and negative values in a Bar Chart, you cannot mix positive and negative values in the 'Stack-by' field, since there is no way to show negative spaces in a positive bar. Try using the Cascade bars option rather than stacking. This allows you to show the net effect of positive and negative bars.

P.S. Similarly, you also cannot split a Pie View by a mix of positive and negative values

I don't agree with this. If you have aggregation involved there shouldn't be a problem as the negative values will be added to positive values anyway.

In the case where you have negative aggregation result it shouldn't be a problem to visualise it as a negative part of the stack bar. As you can see on the attached charts there are some cases where the negative values are displayed.

Why it doesn't work across all the bars?

The aggregation process implied by the split of the bars does take both positive and negative values into account when calculating the total for each bar, but when stacking, i.e. dividing the aggregated split bars as into individual display sub-segments within a given bar, there is no way to show mixed negative and positive stacking sub-elements inside a given bar, even though the aggregate of the bar is a net of positive and negative values. (The same is true of a Pie View, where you cannot mix positive and negative value wedges inside the same pie). If the total is negative and there are only negative sub-segments, they will be displyed, but if the is a mix of positive and negative sub-values the warning is displayed.

The Cascade option spreads the bar stacking elements into multiple aligned sub-bars so both negative and positive stacking elements can be displayed explictly and the alignment shows the net value in the overall bar.

Does it mean that it is impossible to create this type of Stack Bar?

It IS possible to do this, yes. See attached file.

(Once you have stacking or cascading active, the Layout option "Isolate negative+positive stacks/cascades" appears, which you must tick.)

That's great thanks Steve.

PS. I didn't see that option in previous versions.