LCD brightness/dimming control is not changing monotonically

I'm seeing a symptom I can't explain:

I replaced a faulty LCD (a Quanta QD15AL01 rev.5) in my notebook (a Dell
Inspiron 6400) with a "compatible" display (a Chi Mei N154Z1-L01). The
new display's backlight does not respond to changes in brightness correctly:

The brightness can be set from 1 to 8, which should be dimmest to
brightest. With the new display, the dependence is not monotonic: 4
appears brightest, followed by 8, then 1. 2, 3, 5, 6, and 7 are fairly
dim, but show some variation. Even 4 does not appear to be full
brightness. The pattern is perfectly repeatable and stable as I change
the brightness setting.

I've tried two different inverters, including the original inverter.
Both inverters work fine with two other displays I've tried, but both
exhibit the same symptom with this display, so I attribute it to the
backlight responding incorrectly to the output of the inverter, rather
than it being a fault with the inverter. This seems strange, though,
since the backlight is a relatively simple CCFL, I think.

Is it possible that this particular backlight is reflecting power into
the inverter in a funny way that causes the inverter to malfunction for
certain dimming settings?

Is it possible that the inverter is doing PWM and giving the backlight
frequencies it doesn't like for some dimming settings?

Is there any communication from the inverter back to the graphics
card/motherboard, such that it could be telling the software something
confusing about the display? I thought the connection from the
motherboard to the inverter was just an input, with power and dimming
signals.

I am convinced that this is not a software problem, as the symptom
persists while in the BIOS screen, and is unique to this display, which
does appear to be otherwise compatible with the computer.

Thanks much for any advice.
.

Relevant Pages

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