It's a problem if you say it's a problem but I'd be more convinced if you showed us some examples of images where this is an issue and you have no way to get to the color appearance goal desired.
I don't mean to blow things out of proportion. Now that I've had a chance to play with LR, I'm very happy with most if it. But I do think it would be an easier and more versatile tool for me personally if there were an option to have the tone curve leave saturation alone (or adjust it so that it is perceived as being left alone, since in my experience changing the L in HSL results in perceived differences to S, as well -- probably a defect of the HSL model). Would this be the sort of thing that could be addressed by programming a plug-in for LR?
I suspect the reason the saturation isn't being applied 'evenly' is it was coded this way. Thomas has said in the past, it took a lot more engineering work to produce this effect then just applying NO saturation with the tone move. And considering what has to be tens of thousands if not millions of images that have been processed this way for a very long time, it's odd that only rarely do we hear a complaint about it and it usually surfaces after someone has read a rant about this behavior from Mr. Margulis or one of his followers.
I've never heard of Margulis; I see that I've wandered blindly into what I can imagine has been a contentious discussion. My background is just that a) I'm a mathematician with a side interest in graphics, so I think about these things, and b) I've always been frustrated by the hue and saturation shifts in curves in the crappy photo-processing software I've used until now (I sometimes tried splitting to HSL and applying the curves to the L channel, but this usually didn't give great results because of what I mentioned above).
Did you happen to also find this LuLa article:
Thanks for the link! I don't remember having read it when it was posted (and in any case if I had it wouldn't have meant nearly as much to me then as it does now). It's good to have the confirmation that at least LR is locking the hue when the tone curve is applied.
The last bee shot you uploaded (the one with the lower saturation) looks the least desirable to me. But it isn't my image so I defer here to your judgement.
Well, yes, that was my point. To me, the last image looks awful. But of course, I'm not saying one can't get decent results out of LR for this image. Based on the various suggestions and links people have posted, I've now found a couple different ways of doing it, but haven't yet settled on what I like best.