Check your preferences/Presets Tab-
With this un-checked I do not see any sliders move either when pressing [V], or clicking [B&W] on the HSL panel.
I think "when first converting..." means- When YOU first convert an image to B&W. That could be a B&W preset applied (at your request) at import, or when you press [V] or [B&W]
I have this unchecked. It seems to be broken ...
The option to have / not have Auto B&W conversion from the V key operates fine for me (LR 2015.6 version on Win)
But your option (3) is very easy to achieve another way, with a Preset.
I use one which desaturates all the colours in HSL, as my starting point for B&W. That's just my personal preference (since it still leaves the image in colour 'mode' otherwise).
But you could make one which applies B&W only. And un-check Auto Mix, in the definition screen for this preset - or else even edit the Preset in a text editor to make sure it is only activating B&W and not enabling Auto Mix.
Thanks for your reply! I have a preset. But is there a way to assign this preset to a key like "V"? I have thousands of images to process and selecting the preset for every image takes too much time.
Select all the images you want to apply the preset to in Library.
Then click the dropdown menu in the Quick Develop panel and choose the preset under User Presets.
As Richard said, the option to have / not have Auto B&W conversion from the V key operates fine for me also. (LR 2015.6.1 version on OS X 10.11.6)
After messing around with this some more, it seems that the Automix is disabled ONLY when you first change the preference and hit V or after a RESET is done on the photo and you hit V. If I use the B&W button in the HSL panel it works as expected.
WITH AUTOMIX OFF IN PREFERENCES
Hit reset on photo
HSL panel is "Automixed"
Hit reset on photo
HSL panel is NOT "Automixed"
This scenario is NOT consistent. It seems like the V key works ok for awhile but one it breaks it works like the above pattern.
I wonder (speculating only here) whether something has crept into your camera defaults, somehow? Perhaps lying latent there, UNTIL a given image is set to B&W.
Do you still get the same outcome after you've Reset an image to factory ("Adobe") defaults?
I did the Adobe Reset and it still works "Randomly". When I first did the Reset Adobe the V key would not Automix but Using the B&W button would Automix. After several gyrations of the settings they started working in a random manner again. This is NOT an issue I am going to be too concerned about as it is not a big problem and is not repeatable so Adobe would have a hard time trying to fix it. It will be interesting though to see if someone can find a repeatable sequence to make it happen.