

Hmm, that’s strange. Don’t think, it’s supposed to work like that, but that does not either seem like behavior that would manifest from a simple bug.
The words in your screenshot do seem to all be in the English dictionary, well, except for “trotz”, but that’s a German word, so might still be that it somehow takes a dictionary into account.
There might be some dictionary package installed through apt, which might enable that.
Can you check in the Kate settings under Editing→Spellcheck, if any languages show up there? On my system, I actually have none there. Perhaps, if I “fixed” that for me, I might end up with similar completions as you have there…
Also, sidenote: To my knowledge, the T+ icon means that it is a word completion (normally based on words in the document), and not a keyword completion or similar.















Well, you certainly have more of a dictionary available than I do. For me, it looks like this:
(Which, again, might actually be broken on my distro by excessive minimalism. No idea.)
My About→Components section in Kate says this:
You could try setting the “Default language” in the Spellcheck settings to something else and see, if it still completes the same words, just to try to find out whether these dictionaries are connected.
But yeah, might be worth filing a bug report with the Kubuntu devs. At the very least, it would tell them this behavior may not be wanted by everyone, if it is intentional…