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AD8611 changes voltage on input

I have seen an unexpected effect when using the AD8611 with constant voltage levels. Find below a simplified diagram of what's happening. (The circuit is more complicated, so I simplified it even if it does not make much functional sense now).

Before soldering the AD8611, I am setting the S+ to say 2V and the S- to -2V. This works well by tuning the potentionmeter screws, and it's stable. If I now solder the AD8611 comparator, the values on S+ and S- are completely different, for example S+ is 1.3V and S- is 0.7V, both positive! So somehow, the comparator is adding voltage in 'backward' direction.

Does someone know why is this happening? Are the resistances on the input stage too high? Or the voltage difference too large? Or is it a problem that NOTQ is floating?

Thanks in advance!

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