That's not anything specific to LR5.6.....it's been working that way for a long time, at least as far back as LR3.
It's probably working "as designed", though I think the design could be improved....technically you didn't "undo" the B&W conversion, you simply stepped back in the history panel to an earlier edit state, at which point you did the export. Nothing wrong with that, but the unhelpful bit is Lightroom putting the Export step at the top of the history panel, which then reflects the prior edit state. I did put in a bug report on that behaviour in April last year, basically suggesting a change of behaviour such as inserting the "Exported on ....." history step just above the history step that was used for the export, but nothing has happened yet.
Thanks for the reply, Jim.
The thing about this is that it is new to 5.6, in my experience. I have used every LR update going back to 4.1 and 5.6 is the first one that exhibits this bug.
The history is wrong now and it can indicate multiple steps that are not actually there and don't appear in the on screen image or the exported image. I tried to make it simple and show just one step (the B&W conversion) to illustrate it.
Well, as I said I can recreate the "bug" as you show in your original post in LR3 and LR4 and well as LR5.
I don't understand what you mean when you say "it can indicate multiple steps that are not actually there". Are you saying that when you click on any of these steps nothing changes? If there's a step anywhere in the history panel you should be able to click on it and see the image at that particular history point....if that's not happening then that's certainly not something I've seen before.
Hmm, that is strange that your LR has always had a different behavior than mine. I have run on Win7-64 and Win8-64 using every update since LR 4.1. I am wondering if your LR is different or if you are misunderstanding something I have written? Anyway, here are screenshots that show what I see doing something other than an export. This still works the same as it always has. When you undo or back up a step and then do a new step the undone step disappears. I gather that you are saying this also doesn't happen with your LR? Please compare these carefully to the earlier screenshots to see the difference in behavior.