Zero value on the stacked graph is representing as a last non-zero one

I work with a graph panel and face a problem with a zero values.
Due to present my data I use bars, grouped by day. Each bar could contain 3 or less parts which are stacked.
If one part is zero today (and it is clearly seen on the graph that a yellow part is missing), the small window with a daily values still shows the last not-zero value of that part, although the other ones are correct.
Why so? Could you fix this bag pls.