Is this just a case-sentitvity issue? if personas.apellido is a varchar field, then I think that's your trouble. (it would have to be citext in order for "nunez" = "NUNEZ".)
yes, is just a case-sensitivity issue. yes, is a varchar field.
but what i dont understand is why the problem of "insensitivity" is only with ñ (lower). i mean, if i remove my ñ (and subsecuent chars), both querys return the same rows:
