That is correct. You can choose to Ignore a particular item by selecting it, or to stop ignore it in the same manner. You can then take a month off, come back, forget what you ignored, and not know it.
It's not that hard to undo, or to do, but if you forget to check...
So basically the actual ignore list is going to have to be written on a notepad.
Seriously, is it me or do FDev have good ideas and then cripple their usefulness by implementing them in ways which seem to be so far removed from the obvious, logical way you'd think of doing it as to be almost deliberately obtuse?
I mean sure, setting the ignore option whilst something is selected is good functionality in itself because it's immediate and doesn't need you to go into the inventory menu, but surely logic says that with so many materials you need to be able to tell
somewhere what is currently on the ignore list? So use the inventory and a flag system - ignore can be set by either selecting the material in-game and ignoring it (like you say it happens now) or by manually setting the flag on the inventory list (which allows you to plan ahead and set up your ignores before heading off to do something like mining where you may want to temporarily add a block of materials) and cancelling the ignore working the same way - either select the material on-screen and turn ignore off, or switch it off in the inventory list.
You couldn't use the inventory on its own or you'd have no way to remove the ignore setting from a material that you don't have any of but essentially making us reliant on pens and paper or a spreadsheet is just... I don't even.
You know, I honestly don't want to be sitting here making posts like this. There's so much I'm happy about in 3.0 but things like this and the refusal to add proper multiple selection filtering to the galmap just make gameplay feel clumsy where it could be streamlined and have a much more logical workflow. It's like a disconnect coming into play around the way people would actually do things whilst playing the game.