Virtual Masters: "smart glyphs + brace trick" not working


I am trying to make a variable font with a custom axis, in this case is crossbar height like greatly described in the tutorial: Creating a variable font | Glyphs, so I create a virtual master.

The tutorial said that “Unless you want to do some fine-tuning, you will not need to add a Brace layer for the bold master.”
This trick works well when it’s exported as a variable font, but seems wrong in the instance preview in Glyphs and when it’s exported as OTF (it’s exported exactly like the preview).

This happens on the glyphs containing smart glyphs as components, and actually it is fixed and works well if I add a brace layers for each masters.

Any idea why does this happen?
Or if I use my own way to fix it, is it bad if I let all the masters have additional brace layers to keep it work?

Any feedback will be greatly appreciated!

Thank you!