Why in Adjustment Layer Brightness/Contrast in PS checkbox "Use Legacy" does not affect on result?

[Oleg29648376dbg1]

I was surprised to find that when using an adjustment layer, the Legacy checkbox does not switch the function to the old mode. As I understand it, Legacy mode is simply not available through an adjustment layer (except for files created in older versions of PS). Then it's an interface flaw if I can include the selector itself, but it doesn't affect the algorithm?
Note: Through the main menu of Legacy, the mode is correctly turned on and off

[Bojan Živković]

It does switch and produces different result from my testing. Can you show us comparison like one below?

[Oleg29648376dbg1]

Try this attached file
Result main menu:

Result adjustment level:

[c.pfaffenbichler]

Say what? 

[Oleg29648376dbg1]

That's exactly what I'm talking about.
And through Image - Adjustment - Brightness/Contrast with Legacy PS will work correctly according to the old pre-CS3-algorithm.

[c.pfaffenbichler]

Sorry, I had misunderstood your description. 

You are correct that the Brightness Contrast »Use Legacy« setting has a different effect when applied destructively and when applied as an Adjustment Layer. 

[Oleg29648376dbg1]

I would say this - Legacy cannot be applied through an adjustment layer for a file created with at least PS 20.0. At the same time, its checkbox is present and I have a question - what can I turn it on / off - is this a flaw in the interface?

[c.pfaffenbichler]

Checking »Use Legacy« makes a difference (compare my screenshots from before) – so something is being done, apparently not what should be done … 

[Oleg29648376dbg1]

Then it gets even more interesting.

[Oleg29648376dbg1]

I was so focused on the contrast that I did not pay attention - yes, the brightness range changes from -150..150 to -100..100. But CONTRAST, as we have seen, works in an adjustment layer incomprehensibly when Legacy is on.

[D Fosse]

The legacy mode, just to clarify what it is, is a plain offset of values that will clip high and low values. The current mode uses a curve instead, with a falloff so that highlights and shadows are protected.

Either mode is easily reproduced by Levels or Curves, both of which give much more control over the final result. Brightness/Contrast is a blunt instrument.

[Oleg29648376dbg1]

I am in no way questioning the benefits of the current version of Brightness/Contrast.
However, it is often more convenient for me to use Legacy to correct masks through a script.
This post is about the strange behavior of the Legacy checkbox in an adjustment layer.
If it is left in the interface as a signal to the user of the file which of the algorithms will be used by this layer - then why can it be turned on / off since it does not affect anything?