Espada Treble Control Weirdness?

Recently picked up a beautiful natural finish Espada, noticed that the Treble tone control acts very differently depending how the white Parallel/Serial mini-toggle switch is set:

Up = Pickups in Parallel - Treble cut is effective the last ¼ of the control range where it sounds like a wah pedal
Down = Pickups in Serial - Smooth roll off of the high frequencies throughout the control range

Anybody else notice this? Thought I had a bad Treble pot, so replaced it with another (same CTS 500K audio taper), no difference. Checked the wiring, all solid and original.

Appreciate anyone's confirming or denying this behavior as normal and correct.

I don't have an Espada, and I'm not understanding what you mean by a wah pedal sound in this context. However, normally humbucker coils are wired in series. If you put them in parallel the impedance of the pickup will change significantly. As an example, let's say each coil is 5K Ohms. In series the total impedance of the pickup will be 10K Ohms. Wire it in parallel and the total impedance will be 2.5K Ohms. This would change the frequency response of the tone circuit.

Appreciate the detailed response and explanation.

To clarify, in Parallel mode, turning down the Treble pot seems to have no audible effect until last 1/4 or so of the pot's rotation. Turning within that last narrow range, the tone sounds like the faux wah effect you get from rapidly rolling a Telecaster tone knob.

I just checked this out on my Espada and have the same results. Therefore, with an extensive test pool of 2, we can safely say that they all do that.
My experience with guitars that have wide tonal options is that the some combinations don't just have linear tone control.
Oh - and thanks for prompting me to get that guitar out. I haven't played it recently, and have been joyfully reminded how much fun that thing is.

Nearly every electric guitar uses potentiometers with a logarithmic resistance taper rather than a linear taper. Due to this the first 75% or so of the pot movement has only a small effect and the last 25% has the most effect. I suspect this is done so that during live play imprecise adjustments made the artist won't dramatically effect the tone. If you don't like this you can replace the pots with linear taper ones of the same value.

Thanks for confirming that my Espada's behavior is normal.

Played it at an all day jam last weekend, great tones and super comfortable. Glad that G&L went back to a thicker neck with more rounded fretboard edges.