gregarios
Just wanted to let you know the results of my conversation with the team. The behaviour we've seen is a new feature where text fields created in 1Password 8 are word-wrapped as opposed to single-line with ... ellipsis. We haven't tried to upgrade text fields created in 1Password 7 or older to the new style for a couple of reasons: to avoid changing the Date Modified on the items (which is something we want to leave intact and only ever have it changed by you), and so as not to mess with the integrity of your items. Having to "touch" each item to see if it had a custom text field after an upgrade and then change the item internally to give it the new style of text field has a small risk of going wrong, but not zero, and any risk of you losing data or it becoming corrupted is too much for us. Also, some users are in environments where they're using a mixture of 1Password 8 and an older version, and changing these text fields to multi-line could potentially break that backwards compatibility, and again, whenever we think there's a risk to your data, we'll hold back.
Notes fields, as you mentioned, are (and always have been) multi-line, and our experience has shown that most users use that field for anything more than a few words at at time, even using Markdown formatting to break it into sections if necessary.
So with that being the case, I'm told that everything is working as intended – the fields you created in 1Password 7 are the same as they were, and the new style of text fields in 1Password 8 is being used when you add them to items now. If you want to upgrade your custom text fields from the older single-line style to the new multi-line style, the method we talked about of cutting the text from the old field and pasting into a new one would be the way to do that.
Because we have zero knowledge of what's in customers' vaults thanks to our security model, the safest way to for us to implement changes like this is not to try to touch your existing items for the reasons I've shown above. Your stuff is yours and we don't want to change anything without your direct and deliberate intervention.
However, I have suggested a middle ground to the product team: a toggle that allows you to show these older single-line text fields as multi-line without having to change the item itself to do so. This is only a suggestion right now, and there are no guarantees that it'll be implemented, but I can see how it could be useful, so I've asked the question anyway. Let me know if that's something you'd like to see.