From the 8.5.2. Text Spacing Character Classes, halfwidth Kana belongs to "non-ideographic letters". This means that there will be an auto-space between ideographs and halfwidth Kana. This seems like an overlook.

The question is whether they should be "ideograph" or not. Terminology-wise, Kana is derived from Han, so it's closer to ideograph than to non-ideograph. Behavior-wise, I don't think authors expect auto-space between ideograph/fullwidth Kana and halfwidth Kana.

So I think we should classify them not to belong to either "ideographs" nor "non-ideographic letters". I'll check with JLTF about this separately.