Lightroom Classic: B&W mix slider settings lost when converting to colour and back to B&W

When you are in B&W mode and have custom settings in the B&W Mix panel and then convert the image to colour and then back to black and white the B&W Mix panel sliders are all reset to zero.

This is changed from the previous version of Lightroom Classic where the settings were retained. 

This is an issue because if you switch back to colour (maybe to find the colour of what you are changing so you can grab the right slider) and back (to adjust that slider) all your previous settings are lost.

I'm assuming this is a bug that someone can fix for the next version.