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Changing the scale on Tact graph changes the diagram

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I noticed a problem today with one of my speciation diagrams. The diagram script is


> # Tact script, saved Tue Jun 02 2015 by Alex
> data = "C:\Users\Alex\Dropbox\PostDoc\GWB\MY DATABASES\thermo.dspeq06_au_new7.dat" verify
> diagram Au+
> log activity main = -8
> pH = 6
> log activity SO4-- = -3
> swap SO4--/H2S(aq) for O2(aq)
> diagram x = SO4--/H2S(aq)
> speciate SO4--
> x-axis from -10 to 5 increment 2
> y-axis from 0 to 400 increment 50
> mosaic_labels
> line labels size = 23
Tact >
and looks like this (by the way I know this is "correct" because it looks very similar to a published diagram).
But if I change the x-axis range from -10 to 4, to -10 to 0, it looks like this:
Which is clearly not simply a more restricted range of the first diagram. So it seems changing the scale range is doing something other than what I thought it would. Is it a bug or do I just not understand what is happening here?
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Oh, I think SO4 isn't being speciated in the latter diagram. The blue speciation labels are missing for a start. Also, if I put in the range -10 to 0.01 instead, the diagram works as intended:



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Thanks for sending your thermo dataset. We're taking a look at this. In the meantime, as you've discovered, your solution of plotting up to a log ratio of 0.01 works with SO4-- speciated over x in the "in the presence of" section. Alternatively, since you know that H2S(aq) is the dominant form of the ligand below a log ratio of 0, you can swap H2S(aq) for SO4--. That way, you can plot a smaller range if necessary that does not include a log ratio of 0.01.




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