Edit: See comment below by anon2 for an explanation of this behaviour.
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When selecting a colour using the Colour Picker Tool, and then applying it to another shape, the values change slightly.
This seems to happen when HSL is selected in the Colour Panel, but not when CMYK is selected.
It seems to happen with a number of different values, although not all of them.
I've replicated the problem with multiple objects, and multiple colours, on both Publisher (1.8.1)