I haven't faced this particular problem, however I recall solving another sorting problem in a Scatter chart. Unfortunately, Scatter charts can't be sorted in Qlik Sense. To overcome the problem, I created a calculated Dimension using Dual() and assigned the numeric portion of the dual value based on my sorting expression. This trick worked, and my dimension was sorted based on the numeric value.
Try the same here, it might work in a similar way.
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That looks what I got in 1.1. And is it really correct? Look at the 2 light blue bars with a dark red in the middle. 01/06/2015 the lowest light blue is alot thinner than the one above.
Have you some sort of early access to 2.0? Dying to get my hands on that update, hoping they fixed alot of anoying bugs.