Various combinations between deuterated/nondeuterated poly(ethylene oxide) and (fully and partly) deuterated/nondeuterated ethanol solvents were investigated by small-angle neutron scattering. It was found that the deuteration process has strong effects on the polymer solution behavior when approaching the solubility limit upon cooling. Deuteration of the polymer and/or of the solvent can change the character of mixing/demixing and even 'flip' the upper/lower critical solution temperature trends in experimental temperature range.