Version
3.0.4
Reproduction link
https://codesandbox.io/s/priceless-matsumoto-7i99q?file=/src/index.vue
Steps to reproduce
follow the link
What is expected?
The theme in theme-consumer should equal to parent's and child's.
View doesn't sync

What is actually happening?
After the first correct mutation, the view doesn't sync anymore.
Some factors effect the demo.
If you
- don't pass anything to
child's slot, the behavior will be correct
- remove the mixin inside
child, the behavior will be correct
- write parent in
.vue sfc, the behavior will be correct
...
It works in 3.0.2, fails after it.