I've used some of the pens, the ones you have to twist and puncture to reconstitute are pretty adamant about not shaking or causing turbidity in the solution. The Nords are packaged as a liquid, though without any air in vial so they cannot really be shaken and apparently travel wel, though it is recommended not to let it drop out of your fridge. Both the Geno and Nord say keep out of direct light.
Possibly in the poster's case of drawing out and returning solution to the vial it may be increasing the amount of air/liquid interface essentially 'stirring' air into the solution, whereas oxygen is a common pathway of degradation be it food, metal, or in this case medication. Oxidative reactions increase in the presence of UV light, so a tanning bed in hyperbaric chamber is a no go when prepping your batch.
Cheers.
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