Vue 3 cli-service app: "Slot "default" invoked outside of the render function" warning when component with slots is imported from other component - vue.js

Question

MCVE
I have a Tabpane component that takes slots as input. When imported from the template it works as expected.
<Tabpane>
<div caption="I am div 1">Div 1</div>
<div caption="I am div 2">Div 2</div>
</Tabpane>
However when imported from an other component ( Composite in the example ), then it triggers the following warning:
Slot "default" invoked outside of the render function:
this will not track dependencies used in the slot. Invoke the slot function inside the render function instead.
// src/components/Composite.js
import { defineComponent, h } from "vue";
import Tabpane from "./Tabpane.vue";
export default defineComponent({
name: "Composite",
setup() {
const slots = [
h("div", { caption: "I am div 1" }, ["Div 1"]),
h("div", { caption: "I am div 2" }, ["Div 2"])
];
return () => h(Tabpane, {}, () => slots);
}
});

Answer 1

Solved.
The problem was that I called slots.default() from within setup, but not within the returned render function.
Also this component reflected a very beginner approach to reactivity. By now I know better. The old problematic solution is still there in src/components/Tabpane.vue.
The right solution that triggers no warning is:
// src/components/Tabpane2.vue
<script>
import { defineComponent, h, reactive } from "vue";
export default defineComponent({
name: "Tabpane2",
props: {
width: {
type: Number,
default: 400,
},
height: {
type: Number,
default: 200,
},
},
setup(props, { slots }) {
const react = reactive({
selectedTab: 0,
});
return () =>
h("div", { class: ["vertcont"] }, [
h(
"div",
{
class: ["tabs"],
},
slots.default().map((tab, i) =>
h(
"div",
{
class: {
tab: true,
selected: i === react.selectedTab,
},
onClick: () => {
react.selectedTab = i;
},
},
[tab.props.caption]
)
)
),
h(
"div",
{
class: ["slotscont"],
style: {
width: `${props.width}px`,
height: `${props.height}px`,
},
},
slots.default().map((slot, i) =>
h(
"div",
{
class: {
slot: true,
active: react.selectedTab === i,
},
},
[slot]
)
)
),
]);
},
});
</script>
<style>
.tab.selected {
background-color: #efe;
border: solid 2px #afa !important;
border-bottom: transparent !important;
}
.tab {
background-color: #eee;
}
.tabs .tab {
padding: 5px;
margin: 2px;
border: solid 2px #aaa;
border-radius: 8px;
border-bottom: transparent;
cursor: pointer;
user-select: none;
transition: all 0.5s;
color: #007;
}
.tabs {
display: flex;
align-items: center;
margin-left: 5px;
}
.vertcont {
display: flex;
flex-direction: column;
margin: 3px;
}
.slotscont {
position: relative;
overflow: scroll;
padding: 5px;
border: solid 1px #777;
}
.slot {
visibility: hidden;
position: absolute;
}
.slot.active {
visibility: visible;
}
</style>

Answer 2

Slots need to be invoked within the render function and or the <template> box to ensure they keep their reactivity.
A full explanation can be found in this post: https://zelig880.com/how-to-fix-slot-invoked-outside-of-the-render-function-in-vue-3