To reproduce:

• Enable AMC mode in mobile web in the English Wikipedia.
• Go to https://en.m.wikipedia.org/wiki/Dada_Masiti (or any other article)
• Scroll down.
• Click "Categories".
• Click "Add to category".
• Click the search box. Type: Swahili. The autocompletion will suggest "Category:Swahili poetry" as one of the results. Click it.

A button appears:

The appearance and the behavior of this button are very confusing. It's the same color as "Publish", but tapping it does something very different. The meaning of the V mark is confusing. What does it do? Because of the checkmark and the color I thought that I'm supposed to tap it to add it, especially because what I typed was still in the search box. Instead, when I tapped the button, it disappeared. I figured out that tapping the button doesn't add the category. Some suggestions:

• I'd expect the removal to be represented by a separate "X" or "remove" button.
• The V seems unnecessary.
• The color of this button should be different from "Publish".
• Perhaps a label can be added: "These categories will be added".
• My typed string should be probably removed from the search box when I select something. If the intention is to let me select several things that begin with the same characters, then it should be something like a checklist, and the autocompletion list shouldn't disappear.